ORGANIC CHEMISTRY II
ORGANIC CHEMISTRY II CH 310N
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This 179 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 310N at University of Texas at Austin taught by Jonathan Sessler in Fall. Since its upload, it has received 107 views. For similar materials see /class/181865/ch-310n-university-of-texas-at-austin in Chemistry at University of Texas at Austin.
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Date Created: 09/07/15
Transmittance Lecture 6 Infrared Spectroscopy Micmmmrs 4 5 15 3 7 B 9101111131415 10 h CB3CCIERCH3 CK 333333323 0 40 0 3600 3200 2300 2400 2000 1800 1600 1400 1100 1000 300 600 4 Wavemlmber cm Especially Recommended Problems from Chapter 12 124 and 125 126128 1211 and 1212 Knowing spectra we ll cover in class today is essential Doing extra problems off websites to be given at the end of this class is also STRONGLY recommended Infrared Spectroscopy o Vibrational IR spectral region covers 25 X 10396 m 25 micrometers to 25 X 10395 m 25 um Human hair is about 5 O um in diameter 0 Absorption of IR radiation in this region causes bonds to change from a lower Vibrational energy level to a higher one Infrared Frequency Scale 0 IR radiation is commonly expressed in wavenumbers o Wavenumber the number of waves per centimeter cm391 read reciprocal centimeters or Kysers o Expressed in wavenumbers the Vibrational IR extends from 4000 cm391 to 4OO cm 391 100000m cm391 250 pm 100000m cm391 250 um 4000 min1 7 400 cr 1 Transmittance The IR Chart 100 25 Micrometers 20 o 40004 Navenumber crri1 Please know this 400 Molecular Vibrations c Atoms joined by covalent bonds undergo continual vibrations relative to each other 0 The energies associated with these vibrations are quantized within a molecule only speci c vibrational energy levels are allowed 0 The energies associated with transitions between vibrational energy levels for most covalent bonds are from 2 to 10 kcalmol 84 to 42 kJmol Fundamental modes of vibration for a methylene group MIKH g m Wm I H 7 r H r H Symmetric stretching Scissoring Rocking an H A A 3 C4 X H Asymmetric stretching Wagging Twisting Stretching vibrations Bending vibrations Molecular Vibrations o For a molecule to absorb IR radiation the bond undergoing Vibration must be polar change dipole moment a Covalent bonds that do not meet this criterion are said to be IR inactive the CC double and triple bonds of symmetrically substituted alkenes and alkynes for example do not absorb IR radiation because they are not polar bonds Molecular Vibrations o For a simple harmonic oscillator the frequency of a stretching vibration is given by an equation derived from Hooke s law for a vibrating spring 1 M V21tc N Avogadro s number c velocity of light K force constant a measure of the bond strength u the reduced mass Mr Hooke says o The position frequency of absorption of a stretching Vibration depends on the strength of the Vibrating bond direct and the masses of the atoms inverse o The stronger the bond and the lighter the atoms connected by that bond the higher the frequency wavenumber of the Vibration o The intensity of absorption depends primarily on the polarity of the Vibrating bond Chloroform and Deuteriochloroform wwm mmw CDCI3 CHCI3 l i i l l l 1 l l l l 4mm mm mm 15w mm The two major differences in these spectra are l the disappearance of the CH stretching 3020 cm39l and bending 1220 cm39l in the deuterated compound and 2 a shi to the right about 20 cm391 of the other bands relative to the signals for CHCl3 The rst is caused simply by the lack of CH bonds in CDCl3 The second is illustrative of this property that heavier atoms deuterium vs hydrogen Will cause attached bonds to absorb at lower frequencies IR Group Correlation Tables 0 Characteristic IR absorptions for some of the functional groups we deal with most often Bond Frequencycrri1 Intensity OH 32003650 strong and broad NH 31003500 medium CH 28503300 medium to strong CO 16301810 strong CC 16001680 weak CO 10501250 Strong Infrared Spectroscopy w39ave Number cn T39 1200 1100 1300 1 500 3000 500 2000 4000 Wavelength microns Transmittance 3970 100 Numa ma eeeeeeeee 0 M Infrared Spectroscopy Micromelers 4 5 15 7 B 9101111131415 20 11 eugccl cn3 c113 I 36W 3200 2300 M00 2000 1800 1600 1400 1100 1000 300 600 W avennmber cml Frequency Hydrocarbon Vibration cm391 mtensity Alkane CH stretching 2850 3000 strong CH 2 bending 1450 medium CH3 bending 1375 and 1450 weak to medium Alkene CH stretching 3000 3100 weak to medium CC stretching 1600 1680 weak to medium Alkyne CH stretching 3300 medium to strong C stretching 21002250 weak As a General Rule a Qualitative Recollection of Frequencies Works PATTERN RECOGNITION BEATS THE MATHEMATICIAN The Exception Carbonyls Here Knowing more Exact Numbers for the CO Stretching Helps Aldehyde 17401720 cm39l also CH stretch at 28002700 cm391 Ketone 17251705 cm391 Carboxylic Acids 17201705 cm39l also ugly OH stretch at 33002500 cm391 Esters 17501735 cm39l also CO stretches ca 13001000 cm391 Anhydride 2 X CO at ca 1880 and 1740 cm39l also ugly COC stretch at ca 1050 cm391 Acyl halides ca 1800 cm391 a diagnostic high value also CX vibration modes seen at or below 1000 cm391 Amides 16551590 cm39l also NH bending right near this or overlapping for 1 and 2 amides For 1 amides a split NH stretch is seen ca 35003200 cm39l Whereas for 2 amides just one NH stretch is seen 3 amides have no NH s A typical alkane ldrich 03257 CAS11165 9 Can bp 125 127 C Fp 60 F m 199 FW 11423 d 0703 FTNMR 1 2A m mp 57 ngamsao VPFrIR 3 3A v v n A u I u u v I A u c s Characterized by CH stretching in the 30002850 cm391 region But since most organic compounds have CH s this is useless info A typical terminal alkene Aldrich 04606 CAS111660 cams bp 122 123 C Fp 70 F H u FW11222 d 0715 FTNMR11BC c ene 98 mp 401 c ng 14090 VPFF IR 3 19A Characterized by alkene CH stretch in the 31 050 cm391 region Note Internal alkenes lack this Nonsymmetric alkenes have CC stretches at 16701645 cm39l A typical terminal alkyne Aldrich 24438 4 CASI76493 2 C on bp 174 C Fp 122 F Dacy 95 FW 13826 at 0766 FrNMR 3 504A 1 n mp 44 C n5 4270 VPFTIR 3 1582A Note Characteristic high energy CH stretch It Internal alkynes Nonsymmetric alkynes show weak CC triple bond stretch at 21402100 cm39l A typical nitrile fog Aldrich 239930 CAS1097401 quot b p 115 J 13 Fp 62 F Butyronilrila 99 Fr39NMR3 7 1351C 913840 VPFTlR39 3 7950 NEAT NICOLE 205x F74 65 VZAG 217 392 3 5V r 4 7 f5 9 H 2 V 139 11 V Y V S 2A 22 f1 umMv WK Aquot r 7 A V A a s a u a A u c e n x 4900mm 3600 g 1400 3200 3000 2300 2600 2400 2200 2000 see moo anT7tizEo 39 Won V 300 000 7 50 wuauumams Strong CN triple bond stretch makes nitriles a gimme on exams A typical aliphatic alcohol WVVOH Aldrich 112615 CAS111B75 CgHmO bp 196 C Fp 173 105quot 999 FW 13023 v d 0827 FTNMR 1 1653 mp 15 C ng 14290 VPFTIR 3 157B Characterized by fat but pretty stretch at high energy Note also CO stretch at 12001050 cm391 that is also in ethers etc A typical aromatic alcohol of cially a phenol CH3 Aldrich C85751 CAS 10644 5 C7H80 bp 202 C VPFTIR 3 1008A p Cresol 99 2V DC 2 p1 gigol MELT glorious 9 10 1 1 1 2 1 14 15 16quot F224 1 js l l Asia t l 39 J I39IIO gt IOUI l L O J t 2 l l l ll in l l l l lg l y i r v r 7 A r i w t L r l P 39T V i i M I i I i I i i i l 0 H l 1 l V l V 39 l I i E i t y d l y i i l Pquot 1 0 39 39 i t i l i y t i i 1 0 39 l 39 n f m J i i 4 mk 10 39 1 El i 1 l 1 1 v r wws39w 1 l l i i I 0 A A l l 4000 3300 3500 3400 00 3000 2800 2500 2400 2200 Characterized by fat but pre stretch at high energy Note also CO stretch at l 01050 cm391 that is also in ethers etc We also see CC stretching modes in this molecule i 39 i i 39 2000 1800 1 14 1200 1 000 800 600 450 WAVENGl ERS A typical ketone Aldrich 123366 msmmam C7H140 hp 149 1so c Fp 117 F I Emma 98 FW 11419 d 0820 FTNMR 1 6360 mp 35 C n2D 14OBO VP FTIR a 4923 Carbonyl CO stretch at 1715 cm l this is ca 10 cm391 lower energy than for typical aliphatic aldehydes A typical aliphatic aldehyde ldrich 303550 CAS 5435643 RJLH ch ao dOB17 FFNMR 1 731A 55Tlmemylhexanaly 95 14224 ng 14215 VP FFIR a 5540 bp swarms mm Fp116 F Equot MICRONS NICOLET 205x FT IF 25 27 25 25 3 IS 4 05 5 55 6 7 8 0 ll 2 3 Id I5 16 7 I8 9 Z 22 39 m I 1 men Y M big A 7 39 A 39 39 u A v z in W I u I g i I o r W 7H i V 7 74 7 n a l I i ll a V l H m 36W uoc 3200 m 2800 2509 2 DG 2200 2000 800 500 400 200 I000 300 500 A quot AVENUMBEHS Carbonyl CO stretch at 1725 cm39l this is ca 10 cm391 higher energy than for typical aliphatic ketones A typical acyl halide Aldrich 135968 CAS 5176967 02H33r0 bp 75 7 77 C Fp gt230 F new bwmide 99 FW 12295 1 1663 FrNMR 1 11878 mp 96 C n5014500 VPvFFlR 3 7650 K MICRONS NICOLET 205x FHR quot 25 25 27 25 29 I 15 A 45 5 55 E 7 a S m H 12 13 HI IS IS 7 la 9 2 22 391 F 39 r I n x r Aub I v r gnaw 35 n l w r I v m mng ir 7 r r 7 r r ll f l 2 39 39 l l l H 1 3 u quot quotquotquotquot39 39 39 i l39 ll quotquot 31 an w l U E v j K En f 1 1 y Eh I 7 E i l 1 ca i m t V m a 7 1 1 33 o l i i n MW 3500 3600 34m 3200 3000 2800 2500 2400 2200 2000 I m two Sum 200 1000 EDD SM 450 wAvENuMaER r r Characterized by a high CO stretching value c 1800 cm l Also seen are low energy CX modes at S 1000 cm l A typical carboxylic acid MAL Aldrich 153753 CAS12407 2 CusOz bp 237 C Fp gt230 F O anoic acid 995w FW144i22 d 0910 FrNMR 1 7530 mp 16 17 c ng 14275 VPFrIR 3 575A HEAI MICRONS NICOLET ZUSX FLIF u 25 27 23 29 4 as 45 s 55 s 7 a g m n 2 3 4 is is 7 m 9 2 2 x ww N XxA 1 m quot N r 39 39 m i I l 5 i a J I I I i 3 m 1 4 2 a i l i V l i M i l 2 u l no aw i 0 i m 33m 3M MW 3200 3000 280w 2400 2200 2000 500 tam 1 00 200 I000 DD 5047 JDquot W VENUMBERS Has a broad ugly OH stret h that dominates hig energy region Carbonyl signal at 17201705 cm1 also seen as are CO modes A typical ester R NICOLET 205x FL 25 35 27 28 29 J 35 A 45 5 55 2 39 7 B 9 ID H V2 l M 5 5 V7 IE I9 2 2 W p A vim U f l l w I u 39 quot z x w n iii 74 all N1 A 1 l g p 1 i a as n 39 quot l i V39 s 1 1 I r l l l g n In 1 y I 1 r I W l t u 739 39 39i 1 m c E as a V 7 I k i 39 i t if n W7 A I Y m n m i i r m a I 39 l l mu anon 3600 3400 3200 some 2500 25m 2400 2200 2000 f i500 1400 200 mm am 500 150 Note presence of carbonyl 17501735 c 1 if aliphatic and 1730 1715 cm391 if aromatic as well as eith r a broad CO stretch or two distinct CO stretches in the 13001000 cm391 region We see 2 such signals in this example A typical aliphatic anhydride i Aldrich P51478 CAS12362 6 cal1003 bp167 C F9165 Propionic anhydride 97 FW 13014 d 1015 FrNMR 1 11650 mp 13 C ng 14040 VPF rIR 3 761A 1911 11mm macLsrznsxnm Mn 25 21 211 211 1 3 7 sh 1 e 1 11 s 111 11 12 11 11 1s 11 111119 2122 MM Ax so 1 1 J 1 m 111 1 1 1 f 1 11 I111 139 quotl 11 r 1 1 w 4 1 39 1 sol 177 1 S 1 4o 1 1 1 11 quot W l 11 l r 311 1 a I Characterized by a split CO sign a split signal in this region is seen for some amides albeit t 30 ones but for a different reason in the 18351725 cm39 region The presence of an ugly Signal between 1200900 cm 1 gives anhydrides away however A typical primary 1 amide NH Aldrich 0221007 CAS11201871 C 2H25NO FW 19934 Dodecanamme mp 100 10200 quotw AhaWK w M l Qul l l l39 Note presence of socalled amide ba I and II CO stretch N H bending in carbonyl region The split N H stretch seen at high energy is usually diagnostic for a l0 amide Note absence of C0 modes in the 11001000 cm391 region Rules out ester ether anhydride etc A typical secondary 2 amide I H H 30 N CH3 Aldrich M26305 CA5 791531 c3H7No bp 204 206 C F 227 F NMemylace amide 99 FW 7310 d 957 FTNMR 1 1229A mp 26 25quot0 ng 14330 VPFFIH 3 7790 new 25 26 27 2a 29 a 7 NIcuLEnosxrm 2 m u us 6 17 us 9 21 90gt V V a so r W 1N m i quot7 77 A 6 l n gin I 7quot s y n i u i ll 5 I 39 i B a I 39 L i I l 39 quotquot77 a c39 l n l x s so c r 7 A l s i y a 25 7 r i iA m V 7 MW 7 Ar 0 x i i A000 3500 3600 Moo 3 mm 25m 26m 24m 22m 2000 1300 500 I 1200 I000 300 600 I 0 wnvzuuuazns Note presence f poorly resolved amide bands I and II in carbonyl region Broad N H stretch seen at high energy Such signals are also seen in amines by the way although they are often weaker Take a look at Fig 1211 in B amp F for an example A typical 30 amine Aldrich 250996 CAS 2315368 2ChloroN Ndiekhylacelamide 97 quotEA 25 25 27 as 29 3 as n K 3500 35m 3400 3230 3mm 2m 2600 mo 22 2000 55 CSH ZCINO 14962 bp 148 150 C 55 mm Fp gt230 F M1CRONS a 7 VB 1500 WHO I200 Tom 397 39 26b JLNHa CH3 FfNMR 1 1243A VPFTvIR 3 7838 NICOLE39 205x quot45 a u 5 1517mm 2122 m l mm m l V 3 xx 39sua on VVAVEN BEE 7 v W Other than a carbonyl peak at a slightly lower energy than most competing species ie 16501610 cm39l there is not much to to identify 30 amides de nitively Absence of C0 stretch is an important hint as is lack of CC N H etc Web Sites for Reference and Practice Particularly recommended Answers will be made available on the web next week Meanwhile if you are desperate send an email to Prof Sessler or Mr Gross All the answers are lumped together however So please delay as long as you can ie work as many problems as possible before requesting the answers please En an Y s4 mnu 1m nan w 3 a 12 Q3 5 V w Em anavn nermzn Hymns Sam Favnnnsx Hmmy Hnnt Edn DEHHnma A dexs 18 run waw m1edu smnham swcmveruthnn m j 9 Lmkx mavam anemav awmwxumane a exltheWeh aawgna Ewmw mwnwnnessacnnmw ammo Wnlcnmu Ahnut Lhi sit Prnhlams lruanin Structure Elucidatinn A Wnrkhnnk of Unknowns 36111 Unmxsny af N x I 1993 aquot m Ilrllrnllw nnnln pmnmnmnmm III llnH nuunnx nmw nnv wmmnnmn n W anamnanlnf anrnnan nun Ehgnnxlyv E Blnnlmnstrv mm Vnnc lnjnrmwumr WW rm Unwemv nl Nam llama umnmmumm WWW L numHSLnn nu mm MM W mwmmm E25 nuna g1 Dme no Marvel m g m w um in by Darek Bngdal Java appmm displaying malecuhr speckaby Gumaume Cattencuu mm supemsax Henry Rzepa Imperial Ca ege afScxence Technalagy and Medicine 3 4 n 7 m We gdu Mew ngames lam e p V gt 539 Q S 23 u Back mesvd smp Hersh Hume 52m Favames Hmmy Pun mu DeHHame dvess E1 Hipwawchmacuk acaVumv i x ks vant sEa endav andaws pdale raBesAaHhEWeh a aagb andaws aUTWMsanReseathmup aWEED s Zaamm TRANSMITTANCE 9n Zaamhack 2n Zaamam 7m 5m FmdPeak 5U 40 WRevevse 3D 39 End 2 F nlegrale 40m 35m mun 25m mun 15m mun sun Click an a spam m sea wlm m ufahsuninn mighlhe Emma 2 2 clmsen nginn We rm us gm Mew ngames my sh Q S Q Back a smu R h 2 52m Favames Hmmy Pun mu 39 DeHHame dvess 39a WD NehemmnyZ csudh edumewsm Navmmvexwmev mm i x ks Evam sEa endav andawsUpdale raBesAaHhEWeh a aagb andaws aUTWMsanReseathmup aWEED s y F Wu Assgnpem rmmurycampauna Assxgqmennutm Cluck an aresananc and a 0 Wm appearbelaw the appmpmu pmms was ppm Wemel IR Final Thoughts IR measures Vibrational transitions Can be described by classical oscillator theory Frequency proportional to bond strengthmass12 Be able to recognize functional groups Characteristic Group Frequencies can Help OH CN and CO are particularly easy to identify Pattern recognition works best for most situations Speci c memory of carbonyl numbers helps however Pattern recognition works best for most situations Speci c memory of carbonyl numbers helps however Practice with handouts with the book problems and at the online sites nmr ms IR Become skilled at solVing unknowns 1HNMR Review and Clari cation d CHQCO Ha H Hb JC E b 9 8 7 6 5 4 3 2 1 0 ppm Chemical Shift 5 C 50 H 3 a Hc Hb Vinyl acetate Ht Hb Jae Jae l ch 15 Hz l ch 15 Hz lia e10 Hzal HI Iegtl l l Ilt10 Hzal Ie1o Hzal 3 Hz 3 HZ 3 HZ 3 Hz A doublet of doublets A doublet of doublets A doublet of doublets 3 2 I 0 Chemical shi 5 ppm Table 136 Approximate Values of J for Compounds Containing Alkyl and Alkenyl Groups 11 18 Hz Hh H a 8 14Hz H a EH21 HI 8 11Hz 1 Hz o nmwsmmwowwo For two adjacent hydrogen on sp carbons H 1 b 0 20 40 60 80 100120140160180El J12 18HZ w CC J612 Hz For two adjacent hydrogens on spzcarbons Some sp2 Coupling Constants Ha Ha Ha Hb Ha Hh Ha Hb Hb HR CHb Hb H b Jan 612 Hz Jab 0 3 Hz Jab 12 1s Hz J 4 10 Hz Jab 6 8 Hz Jan 14 Hz Jab 0 1 Hz Dustin and Dr Callaway were right 130 Enolate Anion Chemistry Cl CHFCOCHZCH3 COCH20H3 Chapter 19 Lecture 19 Funny slide le over from last lecture THE AUTHOR LIST awe CREDIT mm cm ls we The mm mm The sacandlo last Thaflm 39h39 Fivsl year sluden who muany am amhm Server 939 nder 0quot me expenmenls pe mmed me Ammious assislam ro lfhe Week Made 2 analisxs and wroe me whalg pngI lessor or oslraoc w a Igures Thm 5 being mud amhnr vs Val insnga lhe paper E a ap P S Nichols S Olivcim 9milLB S 3 E N 39 39 39 39 8 9 Tim sacond aulhor Th last authar 1 Grad smaenl nuns 51 th has mg umrlgglfe ggn39 The head hondw Hasn39t d n mmng do wuhlms projecl ma reads Resew even lead the apevbulmey q u bmwasmcluded base 5 r d u quotd hegollhefun quot1 and ms 3 a nelsne hung mound ma mu g g 9amp5 3 among name wu 991th x g meehngs usuany lorlhe an y C 3 paperaocemed j Chtma39xby 31m Y Acidity of protons 05 t0 carbonyls The anion is stabilized by resonsance The better the stabilization the more acidic the oc proton Acidity of a protons on normal aldehydes and ketones is about that of alcohols and less than water pKa 1820 Some are far more acidic ie Bdicarbonyl compounds that have quite low pKa s CH3C02H HF 475 345 90 10 50 16 10 20 50 pKa of some acids and some a protons Some Acid Base Chemistry HB A HAB H H CH3CH20 pKa 25 PK3 16 CH3CCH3 CH3CCH2 20 16 CH3CCH2COCH2CH3 CH3CH20 CH3CCHCOCH2CH3 CH3CH20H 10 16 Enolate Anions Enolate anions are nucleophiles and participate in SNZ reactions Recall halogenation of ketones 39o39 0 F 8N2 0 R R39CH2Br gt RJSCHZR39 Br R R R With simple enolates of normal ketones this can be problematic due to E2 Eliminations However with stabilized enolates it works Enolate Anions function as nucleophiles in carbonyl addition reactions 0 nucleophilic O 26339 JyR addition R L gt R unllRquot R RI Ru V This reaction results in formation of a new CC bond Produces a tetrahedral carbonyl intermediate that can go back protonate or undego E2 elimination What actually happens depends on R s amp conditions Aldo Reaction Aldol This is the First Reaction of this Type Covered in Your Text It is actually a bit complicated and so we Will discuss it after treating related reactions The Acetoacetic Ester Synthesis Versatile Synthesis of Bketoesters and substituted aeetones R If 9 Ii 0 H3C O C C C H C C I CH3 CH3 R39 R39 T he Claisen Condensation o o 1 NaOR39 2 H30 2RCHZCOR39 RCHZCICHCOR39 R39OH R I The Claisen condensation ester with ester condensation makes BKeto esters I Saponi cation and decarboxylation produces the substituted acetone Classical Claisen Condensation o o 0 1NaOCHZCH3 20HscOCHZCH3 2 H3 Two moles of ethyl acetate condense to give ethyl aeetoaeetate 0r aeetoaeetie ester mquEuS m mc on D 050 le II OINI 00050 w ozmozwlmlz Hmzwlooozwoiw Mechanism Step 1 K 0 CH The enolate anion is 2 COCHZCH3 stabilized by resonance I c EHZ COCHZCH3 xv mquEuS m mc N quotmul OImeIOINI OOOINOIHw QV u 05000301 w umzwlooozwoznw mquEuS m o w mul m ozwolozwl 00050 w quot0505 mw mu oEoloEloooEoE lumozwoxw Mechanism Step 3 5 CH3C CH2 COCHZCH3 onoH3 The product is ethyl acetoacetate However were nothing else to happen the yield of ethyl acetoacetate would be small because the equilibrium constant for its formation is small Something else does happen Ethoxide abstracts a proton from the CH2 group to give a stabilized anion The equilibrium constant for this reaction is very favorable mqwg g 920 a oEolmIOOOINOIHw IlmOINOIw ozwolozwlooozon lumozwoxw Mechanism Step 5 O 0 CH3C QH COCHZCH3 In a separate operation the reaction mixture is acidi ed This converts the anion to the isolated product ethyl acetoacetate Mechanism Step 5 5 H II II CH3C CH COCHZCH3 H O H 5 5 H II II Cch clm COCHZCH3 O H H Another example 0 ZCH3CHZCOCHZCH3 Reaction involves bond 1 NaQCHZCH3 formation between the 2 H30 occarbon atom of one ethyl propanoate molecule and the O O carbonyl carbon of the other CH3CH2CCIEHCOCH2CH3 CH3 New Bond Formed Here Carboxylic Acids Chapter 17 O R Cl R CC0 H OH I lt3 0 R C 0 Exam II will cover chapters 151 amp 15218 inclusive Details soon No Of ce Hours Today Sorry Recommended Problems old Recommended Problems new EVERYTHING IN CH 16 EVERYTHING IN CH 17 But if pressed for time start with But if pressed for time start with 16191622 16241626 177178 17121713 16301634 1637 1638 1717 17181723 16401642 16431644 17261727 1650 16541662 1665 1729 17321740 Carboxylic Acids Nomenclature IUPAC IUPAC names drop the e from the parent alkane and add the suf x oic acid If the compound contains a carboncarbon double bond change the in X an to en 06 H 5 H H 3 C H CH 2 CHCO 2 H CC CC H 002 H H 002 H Propenoic acid trans3Phenylpl 0pen0ic transZButenoic Acrylic acid acid acid Cinnamic acid Crotonic acid NomenclatureCommon When common names are used the letters cc 3 y 8 etc are often used to locate substituents N H 2 HOCHZCHZCHZCOZH CH3JZHCOZH 4Hydr0xybutan0ic acid 2Amin0pr0pan0ic acid yHydroxybutyric acid aAminopropionic acid Alanine Naming the Salts To name the salt of the carboxylic acid name the cation followed by the name of the anion two words The anion is named by removing oic acid and adding ate Benzoic acid Sodium benzoate Butyric acid Ammonium butyrate Boiling Points d iw bp 1 atm 31 C 80 C 99 C 141 C Intermolecular forces especially hydrogen bonding are stronger in carboxylic acids than in other compounds of similar shape and molecular weight Physical Properties In the liquid and solid states carboxylic acids are associated by hydrogen bonding into dimeric structures Physical Properties Carboxylic acids have signi cantly higher boiling points than other types of organic compounds of comparable molecular weight they are polar compounds and form very strong intermolecular hydrogen bonds Carboxylic acids are more soluble in water than alcohols ethers aldehydes and ketones of comparable molecular weight they form hydrogen bonds with water molecules through both the CO and OH groups Many Stinkl Physical Properties Water solubility decreases as the relative size of the hydrophobic portion of the molecule increases hydrophilic region increases water hydrophobic region decreases water solubility Infrared Spectroscopy Review A carboxylic acid is characterized by peaks due to OH and CO groups in its infrared spectrum CO stretching gives an intense absorption near 1700 cm39l OH peak is broad and overlaps with C H absorptions Infrared Spectrum of 4Phenybuz anoic acid CSH5CHZCHZCHZCOZH W 0 H and 0 H Sir8W JV 7 v V C mo nosubstituted benzene 3500 3000 2500 2000 1500 1000 500 Wave number cm391 1H NMR OfCarboxylic acids Review The acidic proton in the HO group of a carboxylic acid is normally the least shielded of all protons in a 1H NMR spectrum 8 1013 ppm broadit moves and it is subject to exchange 0 CH2CH2CH2COH J1 ag I 120 110 100 90 40 30 20 10 0 80 70 60 50 Chemical shift 6 ppm 13C NMR OfCarboxylic acids Review The carbonyl carbon on the carboxylic acid group is at low eld 8 160185 ppm but not quite as deshielded as the carbonyl carbon of an aldehyde or ketone 8 190215 ppm Mass Spectrometry Review The McLafferty rearrangement gives a characteristic peak at mz 60 at least for aa unsubstituted alkancic acid systems H C H O McLafferty 2 I rearrangement H C VC 2 CH 2 OH H 1quot H 2 C 0 II I H2 C C CH2 OH mz 60 sammqv 3mm E3 2353 a 558 mun z A01d1ty acids are acids The pKa of typical aliphatic and aromatic carboxylic acids falls within the range 4 to 5 The greater acidity of carboxylic acids relative to alcohols both of Which have oxyanions conjugate bases is because The carboxylate anion is stabilized by resonance Acidity Review ElectronWithdrawing substituents near the carboxyl group increase acidity through their inductive effect H I Bl CI F szCOzH szCOzH inCOzH ampH2C02H H2C02H 476 318 290 286 259 I Acid Strength Acidity Review Substitution by multiple electron Withdrawing groups further increases acidity H3CCOZH H2C1CCOZH HC12CC02H C13COZH PK39 a I Acid Strength 476 286 148 070 Acidity Review The inductive effect of an electron Withdrawing substituent falls off rapidly with its distance from the carboxyl group CI CI CI CinCHzCHzCOz H CH3ampHCH2C02 H CH3 CHz HCOZ H 398 283 pKa 452 I I Preparation of Carboxylic Acids Recall Carboxylic acids can be prepared from the oxidation of alcohols and aldehydes 98 and 1613A CrO3 MOH More H280 H20 butyrio acid buta nol O 0 H2004 o o 1EtOH NaOH Ej H A920 j OH 2 HCI H20 Agl is also used as the oxidant in the Tollen s reagent which was used to generate a silver mirror earlier this year Review Grignard reagents add to CO2 to give acids This is done in 210C to generate benzoic acid 0 O O 0 HCHO Om 39M9quot2ca0 finest 2 ZACH 0 Review Benzoic acids may be made by oxidation of aryl alkanes CHZ CHZCHg oxidized QCHZI H2Oro4 KMnO4 etC39 QCOZH products 28na39ky39 Review Methyl ketones may be converted to carboxylic acids with loss of a carbon atom via haloform reaction E 1 O O xamp e h 312 HO R C gt R C I gt R C HCI3 CH3 NaOH C1 0 I Iodoform Industrial Synthesis of Acetic Acid Old method Generate acetaldehyde and use coba1tIIIacetate to oxidize it to acetic acid HCECH H20 CH2CHOH H3C5H gt H3c E OH H9504 Enol of acetaldehyde C03 Due to rising cost of acetylene production other methods were sought and discovered The Monsanto company developed a process that carbonylates methanol using rhodiumIII salts HI and water Monsanto process CH3OH HI CH3I formation of methyl iodide CH3I RhCO2 CH3RhCo3 amethylrhodium carbonyl complex 0 CH339RhCOI3 CO CH35RhCOI3 gt insertion of CO to give acylrhodium bon o CH35RhCOI3 CH3OH H3c 5 OH CH3RhCOI3 methanolysis of acylrhodium bond gives acetic acid and regenerates methyl rhodium carbonyl complex Note I want you to know this process exists but you need not know details Reactions of Acids Reduction Dccarboxylation Estcri cation Formation of Acid Halidcs Reduction The carboxyl groups is one of the organic functional groups most resistant to reduction it is not affected by catalytic hydrogenation under conditions that easily reduce aldehydes and ketones to alcohols and reduce alkenes and alkynes to alkanes it is not reduced by NaBH4 Reduction by LiAlH4 Lithium aluminum hydride reduces a carboxyl group to a 10 alcohol reduction is carried out in diethyl ether THF or other nonreactive aprotic solvent 0 ll yew GCHZOH OH AOH3 2 H20 Selective Reduction Using the less reactive NaBH4 it is possible to reduce the carbonyl group of an aldehyde or ketone Without affecting a carboxyl group OH O O O u 1NaBH4 l H CCH2CH2CH2 2 H O V CHCH2CH2CH2 39 2 Fischer Esteri cation Esters can be prepared by treatment of a carboxylic acid with an alcohol in the presence of an acid catalyst commonly HZSO4 or gaseous HCl 0 H2 304 3 CH3 ampOH CH3 CH2 OH 2 CH3 OCHz CH3 H20 Ethanoic acid Ethanol Ethyl ethanoate Acetic acid Ethyl alcohol Ethyl acetate Mechanism of Fischer esterificatinn J I a 113 in 39 CH3 R fi Hi39ca ncm Hquot quotn H Key Features ofMeehanism Activation of carbonyl group by protonation of carbonyl oxygen Nucleophilic addition of alcohol to carbonyl group forms tetrahedral intermediate Elimination of water from tetrahedral intermediate restores carbonyl group Diazomethane An easy but dangerous way to make methyl esters HfNElf lt gt H fNN 39 H H Diazomethane ether OH CH2N2 gt R OCH3 N2 carboxylic acid diazomethane methyl ester nitrogen gas Diazomethane Step 1 Deprotonation O 9 RJ OH CNEN RJLO H393NEN carboxylate anion Diazomethane Step 2 nucleophilic displacement 8N2 of N2 an extraordinarily good leaving group by the carboxylate anion ii SN2 E R 39039 gt R OCH3 N2 H carboxylate anion methyl ester nitrogen gas Fischer Deesteri cation Esters can be hydrolyzed by treatment With aqueous acid This is just the reverse of the esteri cation reaction Be sure you know mechanism 0 O amp H2 804 CH3 OCHZCH3 H20 g CH330H CH3CH20H Ethyl ethanoate ethanoic acid ethanol ethyl acetate acetic acid ethyl alcohol Base Hydrolysis of Esters Hydrolysis of an esters is aqueous base is called saponiflcation Each mole of ester hydrolyzed requires 1 mole of base for this reason ester hydrolysis in aqueous base is said to be basepromoted not catalyzed 0 RCOCH3 NaOH gt Rco39 Na CH3OH Hydrolysis of an ester in aqueous base involves formation of a tetrahedral carbonyl addition intermediate followed by its collapse and proton transfers Saponi cation wk 3 R dew 2 OH methyl ester example for study of mech 725043 gt R 939 CHsoH V carboxylate methanol anion in this example Saponi cation of F at 0 ll CH OH I EHZ O C R NaOH I 2 R C O C H H OH CHZO R CHTOH Fat 0 glycerol R 2 CH3 CH21 6COOH Fatty Acid Salt II Soapquot Stearic Acid CH3CH27CHCHCH27COOH 0161C acid etc Soaps and Detergents Surface Active Agents surfactants CH3CH216COO Na soap 0 ll CH3CH211 O39Na Anionic detergent O 99 6CI QCH2NCH215CH3 Catlonle Detergent CH3 Soap micelle 1 5 fr at 54 A snap Na Polar head Nnnp lar litail39 Crass section of a soap micelle in water Soap micelle with a dissolved grease droplet Snap micelle with dissolved greas Grease Soap the solution to pollution is dilution Decarboxylation Deoarboxylation loss of CO2 from a oarboxyl group Most carboxylie acids if heated to a very high temperature fried undergo thermal deoarboxylation Most carboxylie acids however are quite resistant to reasonable heat and melt or even boil Without deoarboxylation Decarboxylation Exceptions are carboxylic acids that have a carbonyl group beta to the carboxyl group this type of carboxylic acid undergoes decarboxylation 0n mild heating 0 9 O CH3Bd 8 H2c0H M CH3dCH3 co2 3Oxobutanoic acid Acetone Acetoacetic acid This reaction will be really important when we get to chapter 19 Decarboxylation Decarboxylation occurs readily if there is any carbonyl group beta to the carboxyl Malonic acid and substituted malonic acids for example also undergo thermal decarboxylation 0 140150 C HOCCHZCOH gtCH3COH co2 Propanedioic acid Malonic acid This reaction will be really important when we get to chapter 19 Decarboxylation Thermal decarboxylation of a Bketoacid involves rearrangement of siX electrons in a cyclic sixmembered transition state H H o 0 ME 2 a 1 H3C o gtH3C CH 0 CH3 CC 3 002 H H enol of A cyclic sixmembered a ketone transition state This reaction will be really important when we get to chapter 19 Exam II will cover chapters 1518 inclusive but only 151 and 152 Extra Of ce Hours Today and Monday 3 430 pm in both cases Recommended Problems new Recommended Problems new EVERYTHING IN CH 17 EVERYTHING IN CH 18 But if pressed for time start With But if pressed for time start with 17717817121713 1861881891811 171717181723 18318418191821 17261727 18241826 1827 very useful 1729 17321740 1828 1829 amp 1830 as mechs 18321834 18391841 18451853 Chapter 18 Carboxylic Acid Derivatives We will study ve classes of organic compounds derived from acids by dehydration Under the structural formula of each is a drawing to help you see its formal relationship to the carboxyl group O O O O O R3CI RcoER39 RcOR39 RICNH 2 RC EN An acid chloride An acid anhydride An ester An amide A nitrile o o I I o mm II I The enol of an amide Acid Chlorides The functional group of an acid halide is a carbonyl group bonded to a halogen atom Among the acid halides acid chlorides are by far the most common and the most Widely used 0 O 0 cx CH3 CCI QCCI Functional group Acetyl chloride Benzoyl chloride of an acid halide Acid Chlorides Prep Acid chlorides are most often prepared by treatment of a carboxylic acid with thionyl chloride 0 CH3CHZCH2d0H SOCI2 gt Butanoic acid Thionyl chloride 0 02 Butanoyl chloride Acid Chlorides Prep The mechanism for this reaction is divided into two steps Step 1 39OH a poor leaving group is transformed into a chlorosulfite group a good leaving group 9 O i i ll RiIOH ClSCl gt R C O S Cl HCI YJ A chlorosul te group Acid Chlorides Prep Step 2 Attack of chloride ion gives a tetrahedral carbonyl addition intermediate which collapses to give the acid chloride 6quot E R gl kOj S CH A tetrahedral carbonyl addition intermediate gt RCCI 02 Cl Sulfonyl Chlorides Replacement of the OH in a sulfonic acid by Cl gives a sulfonyl chloride 0 0 H CH 3 EOH CH 3 CI O Methanesulfonic Methanesulfonyl chloride acid Mesyl chloride MsCl R 0 H H 3 C O H H 3 C CI O O pToluenesulfonic pToluenesulfonyl chloride acid Tosyl chloride TsCl Acid Anhydrides The functional group of a acid anhydride is two acyl groups bonded to an oxygen atom the anhydride may be symmetrical two identical acyl groups or mixed two different acyl groups To name replace acid of the parent acid by anhydride QEOEQ CHJ39EOEQ Acetic anhydride Benzoic anhydride Acetic benZOiC anhydride Naming Acid Anhydrides Cyclic anhydrides are named from the dicarboxylic acids from which they are derived Only the symmetrical anhydrides are of interest to us at this time 0 O o 0 O O Succinic Maleic Phthalic anhydride anhydride anhydride Amides The functional group of an amide is an acyl group bonded to a nitrogen atom IUPAC drop oic acid from the name of the parent acid and add amide If the amide nitrogen is bonded to an alkyl or aryl group name the group and show its location on nitrogen by N i i CH3CNH2 QCNHZ CH3CNHCH3 Acetamide Benzamide NMethylacetamide a 1 amide a 1 amide a 2 amide Amides Nomenclature Cyclic amides are called lactams Name the parent carboxylic acid drop the suf x ic acid and add lactam 3 NH H3C 3Butanolactam BButyrolactam I O B321 4 y 56NH 8 a 6Hexanolactam 8Caprolactam Nitriles The functional group of a nitrile is a cyano group IUPAC name as an alkanenitrile Common drop the suf x ic acid and add onitrile CH3CEN Q CEN Ethanenitrile Benzonitrile Phenylethanenitrile Acetonitrile Phenylacetonitrile Nucleophilic Acyl Subst The most important reaction of the rst four classes of compounds acid halides acid anhydrides esters and amides is nucleophilic acyl substitution The mechanism involves an addition elimination sequence and results in the substitution of one nucleophile for another Nucleophilic Acyl Substitution With an anion as nucleophile 65 R Y O C o x lg X R X Y R Y This is a very IMPORTANT general reaction Understanding the mechanism allows one to explain and predict a large body of organic chemistry Nucleophilic Acyl Substitution with uncharged nucleophile 6zH fl HY R H fl C C R f R Y Y Protonated intermediates N0 anions in neutral or acidic media Characteristic Reactions Here the leaving group is shown as an anion to illustrate an important point the weaker the base the better the leaving group 39039 39 NR2 9R OCR x Increasing leaving ability Increasing basicitv Characteristic Reactions Halide ion is the weakest base and the best leaving group acid halides are the most reactive toward nucleophilic acyl substitution Amide ion is the strongest base and the poorest leaving group amides are the least reactive toward nucleophilic acyl substitution 0 o o o o I I I RdNH 2 REOR39 R o a RI39JX Amide Ester Anhydride Acid halide Reactivity toward nucleophilic acyl substitution Relative reactivities of carbuxyl derivatives gt 3 E 3 a a u an E m a v a 9 u G Reactions ofAeyl Derivatives W Can React to Give Others Below it RCCI O SO can each ofthese RCOCR39 W 1 I RCOR O RENR Reactions ofAcyl Chlorides Acyl chlorides react with alcohols to give esters 0 ii RCCI R39OH RCOR39 HCI Please review the nomenclature of esters see page 644 Reaction With Alcohols Acid halides react with alcohols to give esters acid halides are so reactive toward alcohols no catalyst is necessary If the alcohol or resulting ester is sensitive to HCl reaction is carried out in the presence of a 3 amine to neutralize the acid 0 gt Butanoyl chloride Cyclohexanol O CH3CHZCszoO HCI Cyclohexyl butanoate Reactions of Acyl Chloridcs Acyl chlorides react with carboxylic acids to give acid anhydrides O O O 0 RCOCR39 HCI RCCI R39COH H CH via R Cl OCR39 CI Example O W CH3CH25CC CH3CH25COH pyridine W W CH3CH25COCCH25CH3 Reactions ofAcyl Chlorides Acyl chlorides react with ammonia and amines to give amides 0 if RCCI R39ZNH RCNR392 Cl H C via R Cl NR392 CI EXQSEQ o U u U ZmOI IMO Reactions OfAcyl Chlorides Acyl chlorides react with water or base to give carboxylic acids carboxylate ion in base 0 ii RCOH HCI RCCI H20 0 0 RCCI 2Ho Rco Cl H20 EXQSER QNERQNSNENW O 091 on IMO omImOINOOI 9 Reactivity Acyl chlorides undergo nucleophilic acyl substitution much faster than the correspnding alkyl chlorides C6H5CC CGH5CHZCI Relative rates of hydrolysis 25 C 1 0 1 Anhydrides Reaction With Alcohols Acid anhydrides react with alcohols to give one mole of ester and one mole of carboxylic acid 0 CH3 0 II I 3 COCHCHZCH3 o HocHCHZCH3 ltj 90H 0 o Phthalic 2Butan01 secButy hydrogen anhydride secButyl alcohol phthalate Reactions of Acid Anhydrides Anhydrides react with ammonia and amines to give amides o o o 0 RCOCR R39ZNH RCNR392 R c o H H C via R Cl ENR392 0 CR Reactions of Esters Esters react with ammonia and amines to give amides 0 if RCOR R39ZNH RCNR392 ROH H C via R Cl NR392 OR Reaction of Esters With OH 39 We ve Seen This Already Hydrolysis of an esters is aqueous base is called saponi cation Each mol of ester hydrolyzed requires 1 mol of base for this reason ester hydrolysis in aqueous base is said to be basepromoted not catalyzed o 0 H20 RCOCH3 NaOH gt RCO Na CH3OH Hydrolysis of an ester in aqueous base involves formation of a tetrahedral carbonyl addition intermediate followed by collapse and proton transfer nucleophilic acyl substitution Saponi oation Basepromoted ester hydrolysis R l OCHs 39z39dH RLPBCHs OH methyl ester quot example for study of mech carboxylate anion Note Consumption of base makes reaction essentially irreversable CH3OH methanol in this example Proof that Murphy s Law is Reproducible Hydrolysis ofAml39deS Hydrolysis of amides is also irreversible In acid solution the amine product is protonated to give an ammonium salt RCNHR39 H20 H 39 RCOH R39NH3 Hydrolysis ofAml39deS In basic solution the carboxylic acid product is deprotonated to give a carboxylate ion This makes the reaction irreversible RCNHR39 H0 RCO R39NH2 Hydrolysis of Amides in Acid Hydrolysis of amides in aqueous acid requires 1 mol of acid per mol of amide 0 CH CH HcquotNH H o HCI H20 3 2 2 2 heat Ph 2Phenylbutanamide 9 CH3CHZcHCOH NH4cr Ph 2Phenylbutan0ic acid Acid Mediated Hydrolysis of Amides Acidcatalyzed hydrolysis of an amide is divided into three steps Step 1 protonation of the carbonyl oxygen II 6H 6H R CNHZ HCO H gt u r 39139 R c NH2lt gt R CNH2 H20 Resonancestabilized cation Acid Catalyzed Hydrolysis of Amides Step 2 addition of H20 t0 the carbonyl carbon followed by proton transfer DH proton transfer quotOH II R W O H gt R C NHZ MgtR C NH3 I I 39 Tetrahedral carbonyl addition intermediate Acid Catalyzed Hydrolysis OfAmideS Step 3 collapse of the intermediate coupled with proton transfer to give the carboxylic acid and ammonium ion 0 RH o JH f 0 on R I NH3 R I NH3 RCQH NH4 9H 9H Base Catalyzed Hydrolysis OfAmideS Hydrolysis of an amide in aqueous base requires 1 mol of base per mol of amide O 0 H20 ll CH3CNH NaOH heat CH3CO Na H2N NPhenylethanamide Sodium acetate Aninne Base Catalyzed Hydrolysis ofAmideS Hydrolysis of an amide in aqueous base is divided into three steps Step 1 addition of hydroxide ion to the carbonyl carbon z EIS R Ciillzjz H gt R CI Hz 9 H Tetrahedral carbonyl addition intermediate Base Catalyzed Hydrolysis ofAmideS Step 2 collapse of the intermediate to form a carboxylie acid and ammonia 0 0 RNH2 H o H R4 NH3 36H V4 OH QH Tetrahedral carbonyl addition intermediate Base Catalyzed Hydrolysis OfAmideS Step 3 proton transfer to form the earboxylate anion and water Hydrolysis is driven to completion by this acidbase reaction 0 R4 7amp5 gt R4 H j H 9H Preparation of N itriles By dehydration of amides uses the reagent P4010 often written as P205 0 CH eHyzNH P4010 CH CHCN 3 2 2 200 C 3 2 Addition ofGrignard Reagents t0 Nitriles lng lH R39M x H o RCN g RCR39 2 RCR39 diethyl ether Grignard reagents add to carbonnitrogen triple bonds in the same way that they add to carbon oxygen double bonds The product of the reaction is an irnine Addition ofGrignard Reagents t0 Nitriles rhing lH R39M X H o RCEN g RCR39 2 RCR39 diethyl ether H30 Imines are readily hydrolyzed to ketones Therefore the reaction of Grignard fl reagents with nitriles can be used as a RCR synthesis of ketones Dr Boul is looking for bright and enthusiastic UG students to participate in research in cutting edge Molecular Nanotechnology The project will involve the study Carbon Nanotubes as Supramolecular Organic Nanoscale Molecules This will involve organic synthesis and analysis of nanoscale materials Applications range from the development new electronic materials to potential treatments for human disease The position is unpaid but credit in 206 or 369K is possible If Interested Please Email Dr Boul pboulcmutexasedu Carbohydrates Chapter 25 Sessler Introduction Carbohydrates are the most abundant organic compounds in the plant world They are storehouses of chemical energy glucose starch glycogen They serve as components of supportive structures in plants cellulose and connective tissues in animals acidic polysaccharides They are essential components of nucleic acids Dribose RNA and 2deoxyDribose DNA Carbohydrates make up 34 of the dry weight of plants and are one of the major sources of energy for animals even though once consumed the energy is stored elsewhere Formula for carboydrates CnHZOIn like a hydrate of carbon example Glucose blood sugar C6H1206 or C6HZO6 Sucrose table sugar CIZHZZO11 or C12HZO11 This formula isn t always applicable but has become common chemical terminology and persists The majority of carbohydrates are polyhydroxy aldehydes and ketones Therefore the chemistry of carbonyls and hydoxyl groups dominates here Monosaccharides Monosaccharides CnHZHO11 One of the carbons of these compounds is either a ketone or an aldehyde The suf x ose is added to a molecule that is a carbohydrate and pre xes tri tert and pent are used to indicate the number of carbons trioses to octoses are the most common monosaccharides with the chemistry of pentoses and hexoses dominating Monosaccharides containing an aldehyde functionality are called aldoses and those that contain a ketone functionality are known as ketoses There are only two trioses CHO CIDHZOH cHOH 00 I CH20H CHZOH Glyceraldehyde Dihydroxyacetone an aldotriose a ketotrlose Often common names are used exclusively with carbohydrates and are rmly rooted in the literature This is the case for glyceraldehyde which has the IUPAC name l3dihydroxypropanal While okay for a small molecule like this the IUPAC names become unwieldy for bigger systems and are never found in the biochemical or biological literature As such common names will be used throughout this discussion of carbohydrates Fischer Projection Formulas Glyceraldehyde contains a stereocenter and as such exists as two enantiomers QHO QHO HgtCltOH HOgtCltH CHon CHZOH R G1yceraldehyde SGlyceraldehyde Chemists use a twodimensional representation called a Fischer Projection to show the con guration of carbohydrates To write a Fischer projection draw the 3D molecule so that the vertical bonds are away from you and the horizontal bonds are pointing toward you Then write the molecule as a 2D gure with the stereocenter at the point where the bonds cross HO CHO RGlyceraldehyde H O H gt H O H RGlyceraldehyde 3D represntation CHzo H CHZOH Fischer projection Convert to Fischer projection The vertical segments of the Fischer projection represent bonds away from you and the horizontal segments represent bonds toward you Keep in mind that this is a 3D representation and so groups may not be interchanged without stereochemical consequences D and L Monosaccharides Although the RS system is widely accepted today as a standard for designating stereochemistry the con guration of carbohydrates amino acids too is designated by the DL system This nomeclature system was proposed in 1891 by Emil Fischer It was known that one isomer of glyceraldehyde rotated polarized light 1350 and the other l35 Fischer arbitrarily assigned the dextrarotary compound as D and the levarotary compound as L He had a 5050 chance of being correct and in 1952 his assignment was shown to be accurate by Xray diffraction anal sis y Note Common AA s are L common sugars D CH0 CH0 HOH HO i H CHZOH CHZOH DGlyceraldehye LGlyceraldehye a 1350 a 135 D and Lglyceraldehyde serve as reference points for the assignment of the relative con guration to all other aldoses and ketoses This reference point is the stereocenter furthest from the carbonyl group Because this stereocenter is always next to the last carbon of the chain it is called the penultimate carbon Therefore a D monosaccharide has the same configuration at its penultimate carbon as Dglyceraldehyde its OH is on the right of the Fischer projection If we examine a table of all the Daldo and D2ketotetroses pentoses and hexoses we see the name consists of three parts 1 The letter D speci es the con guration of the penultimate carbon 2 Pre xes such as rib arabin and gluc specify the number of carbons in the molecule and the con guration of all the other stereocenters in the monosaccharide 3 The suffix ose designates that the compound is a carbohydrate Part 2 is hard and there is no short cut I know other than to sit down and memorize the players involved DAldoses mm Mummmumnmmm mmnmnom a WWW mm m Dam m o 0o W mm W Wm aw m m m m mm mm m mm Dketoses 39l uhl 2 Onnllgumllnnal Mamth Among mp lwmpric nZKelapenloses and uZKemhexoses H H CHYOH Dmhulmz ix101 TI20H CHEOH an on CLO CLO CLO x OH HO 1 H OH Ho 5 x or H HO 2 Ho 5 H Bil H 39oIi H uh H OF CHXOH C32 1 2 Dmee DFmthe base DTagnmse Tn magnum n 4 mm 70H 0 m Puqu adam u mwn m my Amino Sugars Amino sugars contain an NH2 group in the place of an OH group Only three amino sugars are common in nature Dglucosamine Dmannosamine and Dgalactosamine NAcetylDglucosamine is a component of many polysaccharides including chitin the hard shelllike exoskeleton of crustaceans and shell sh CH0 CH0 CH0 CH0 H CH3 H NH2 H2N H H NH2 H N lt Ho H HO H Ho H Ho H O H OH H OH Ho H H OH H OH H OH H OH H OH CHZOH CHZOH CHZOH CHZOH Dglucosamine DMannosamine DGalactosamine NAcetyIDglucosamine Physical Properties of Carbohydrates Monosaccharides are generally Colorless crystalline solids Soluble in water good H bonds between OH groups and water Slightly soluble in ethanol but insoluble in nonpolar organic solvents like ether chloroform and benzene Most are sweet to the taste see relative sweetness table
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