Week 7/Lecture Notes
Week 7/Lecture Notes CHEM 2321
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This 8 page Class Notes was uploaded by Hayley Lecker on Friday October 9, 2015. The Class Notes belongs to CHEM 2321 at University of Texas at El Paso taught by Dr. James Salvador in Fall 2015. Since its upload, it has received 56 views. For similar materials see Organic Chemistry I in Chemistry at University of Texas at El Paso.
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Date Created: 10/09/15
Organic Chemistry Week 7 Important Information Professor s Email isalutepedu Class Website organicutepeducourses2324 Class Code Ebook utep232Xfall2015 71 Acvclic Aldehvdes and Ketones reference pages 298300 71 Naming CarbonOxygen Double Bonds Most vestile functional group is the carbonyl group There are 3 general types of carbonyl groups aldehydes ketones and carboxylic acids and their derivatives 0 0 H H ii RC H RC Iiir Aldehyde Keteirie Cerbexylie eeide and Cerbexyllie eeiti derivatives Aldehydes are double bonded to oxygens at the end carbon and that carbon also contains single bond to hydrogen The frequencly used abrravation for aldehyde is CHO To Name an Aldehyde 1 Determine parent chaincompound 2 For straight chain alkanes drop the final e and replace with al Call compound by the name alkanal CH3CHj2CHZCH is e e written as CH3CH2CH2CHO Butane 3 To number the substitents assume carbon With aldehyde is group 1 Omit the number 1 when naming only use numbering for substitents O 3 Methylpentenell 4 For an aldehyde group attached to a ring or if another functional group has priority use suffix carbaldehyde sometimes written as carboxaldehyde Cyclohexa ecarbaldehyde Ketones have an oxygen double bonded to a carbon however it is in between two alkyl groups To Name a Ketone 1 2 3 Determine parent compound Drop the final e and replace with one this makes the name alkanone Because of the oxygen bonds being somewhat in the middle give it the lowest possible number if CH3CH2CCH3 ZBautanone Another way to name is by naming the two alkyl groups on eitherside of the cabonxyl group as substituents then add ketone so the name would be alkyl alkyl ketone Example of this is 2butanone is often called ethyl methyl ketone The two alkyls are listed alphabetically When another functional group has priority over a ketone regard oxygen as a substituent designating with prefix oxo o CH3CHer fiHCCHZCH3 K 4Methyll3hexanone o o C ll 0 U CH3C CH3CH Dicyclohexyl ketone 3UXObutanal 3Methylcyclolhexanone Example of naming using IUPAC rules e e lglPhenylethainone This compound is commonly called acetophenone 75 Mechanisms The Acid Catalyzed Synthesis of the Ketal of Cyclohexanone and Ethane 12diol referance pages 310319 75 Addition of Water and Alcohols The nucleophilic additions reaction of a carbonyl group in aldehydes and ketones with water is a rabidly revesible equilibrium and prudces a class of compounds known as hydrates i am RCRquot H12 1 Kiri3R OH Acidcatalyzed reaction has 3 steps The first step involves the pritonation of the carbonyl oxygen in a 13electron pair displacement operation This simply means a hydrogen from an acid so H is added to the double bonded oxygen The second step is a nucleophlic attack by water on the carbonyl carbon This is when the double bond to oxygen is broken and the oxygen from the water bonds to carbon The third step is the loss of a proton to form the hydrateThis is where the second oxygen on carbon losses its extra hydrogen thus the acid that started the reaction is dispelledThe 2quot l and 3rel steps are 13electron pair displacement operations i To HOH2 R quotj 39o 3939C0 H20 R39 H The position of the equlibruim for the nucleophilic addition of water to aldehydes and ketones is based on the size and number of groups attached to the carbonyl carbon As the carbonyl group becomes increasing hindered it favors the substrate Aldehydes are more hydrated that ketones Table 1 Shows Relation of size and eqilibrium Carbonyl KB Reaction Compound at 2530 at equilibrium l 41 9995 2 CHECH 18 X 10 50 l 3 GHQZCHCH 12 X 10 32 3 CHBECCH 40 X 10 20 CHSCCHE 25 X 10 014 1 8 4 CHmCCCmHS 31 X 10 17 X 10 The table above shows that the Ke and percent of reaction to form a hydrate decreases as the size of the groups attached to the carbonyl carbon increase This is due to steric hinderance A second factor is the electronic effect of the alkyl groups attached to the carbonyl carbon because alkyl groups are weakly electrondonating it reduces the partial charge on the carbonyl carbon thus decreasing its reactivity A strong electronwithdrawing substutient attached to the carbonyl carbon can shift the equalibrium to the product Conside CF3 this is a strong electronwithdrawing The negative end of the dipole moment for each of the CF bonds is the flourine atom 3 of these bonds creates a large partial positive charge on the carbon this in turn attempts to withdraw more electron density for the carbonyl carbon Acetone has only a minute amount of hydration in constrast to hexafluroacetone which is almost completely hydrated ii ClF3CClF3 H20 Econ Xe 22 x 104 on Hydrates are unstable and most cannot be isolated Two hydrates stable enough to isolate are methanol formaldyhyde and trichloroethanal choral hydrate Methanol is a gas at room temperature and its boil ng poin 395 21C chemists use it as a 37 aqueous solution of the hydrate this is called f rmalin It39i39s 39o qqeverse biological If speCImens CH3CH2 Chloral with H20 has a f 3x104 a very large nu ber and it is i olated in a stable solid with a mel mlg point f57C 39 9 f HM f IH oH 31ng 1 Fomalin Chloral hydrate v A reaction that is equivalent to hydration takes place between ketones or aldehydes and an alcohol The Produce is hemiacetals Hemiacetals are revisable and follow the 3 similar steps of a hydrate The 1st step involves an acidcatalyzed reaction this is the protonation H addition to the carbonyl oxygen in a hetergenic bond Protonation of oxygen enhances the ectronphiliaty of the carbonyl carbon ax CH3CH2H CH3 lHydroxypmpyl methyl ether A Hemjaeeltall 64 CHgCHZCH CH30H The 2ncl step a nucleophilic oxygen of the alochol adds to the carbonyl carbon of the resonance hybrid in a 13electron pair displacement operation The reaction consumes a proton to intiate the reaction then release it at the end of the sequence e3 x seen 7 Eli 5 V 5 1 V V LII CHB39CHZ 352 1 CHEQH C grmgCH V glII HI LII j if a Ell 13cm 35 CH3CH1EZH gaH Hemiacetal formation is basecatalyzed Many bases are effective most commonly used is hydroxide ion OH Ii 11 39ll eli I if g H t me CH3 Hzm 39Ihe metheaide inn11 adds tn the earheujrl greup ref pre paua fanning the enter at the hemiaeetal ii339 r CHEW a ea eageagea Ihr mj Finally the hemiacetal a n eh reacts with a meleeule ef methane generatith amether metheaide ire11 and the prettuet hemiacetal EE 1 e ea I EEEUIJICITH ma a to Most hemiacetal formation reactions are not energenically favorable so heat energy must be added for the reaction to occur The equlibrium constant for most hemiacetal reactions is less than 1 the exception to this is when reactions form a 5 or 6 membered cyclic hemiacetal These proceed without added energy because of the stability that 5 or 6 membered rings have H Um x 3H e ea Cyclic hemiacetals only occur in natural compounds Glucose contained a 6memebered cyclic hemiacetal A ring is formed by an OH group on C5 of a straight chain of glucose An OH is on every carbon from C2 to C6 H Gaze1 DH H D A r H CllI39 3 x I i a v DH UH UH H 1H H H rm WEE 31m Gimme When 2mol of alcoon and a cataylic quantity og acid are added to the carbonyl group of an aldehyde or ketone an acetal is formed with involved 2 steps 1st Step Reactions forms hemiacetals so follow those steps first 2ncl Step Hemiacetals reactions with 2ncl alcohol the cataytic H ion hydrogen ion added to the 1st oxygen of the hemiacetals in a heterogenic bond forming operations this can hadd to any oxygen in the reactions If it bondes to the oxygen bonded to the hydrogen this results in water loss and a carbon cation this will be the path on the left in the example below If it adds to the oxygen bonded between 2 carbons the right path reactions leds to loss of alcohol and regenerations of original carbonyl group Ky immin h1 l t l tr hga quot x at i L I 39 IEEEhC gy g EEEEEC4 l i I k H f quot391 17 I I 7 ll Eh E g F4F Eh lhfk fh H H After resonacestablized cation forms it reacts with a molecule of oxygen to produce acetal IEEEIIEEIJ yirh qu ap Eh i f i I i I w grear 1 4ilE1 i magma II13 ma a Lecture Notes for the Week To find the number of moles an reaction will be at a certain point use the following equa on x2 10 pKafpKab K 11 3002 35 Example pKa 151 H H N pKa 108 1I l2 N3 N4 if RH H H H O O 05 mole 500 mole Given the number of moles of reactants underneath the reaction to the nearest tenth how many moles of the first reactant will be left at equilibrium 01 b 02 c 03 d 04 e not ad We have the pKa forward and backward so 1039153911 39850E395K x2 5 x500 x From here you should plug in the x numbers and if it returns the K of 50E395 it is your number The answer ends up being A 10 pK fpK b 5013 5 Electronegativty increases as you go up the and over on the periodic table The pKa goes up as you go down the perodic table this means acidity increases as you go down Small atoms are called hard ionic Big atoms colvalant are called soft Atoms wanted to be bonded to the same size or about the same size So as you go down the perodic table there is a size mismatch in the atoms increase so the bonds become weaker
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