Week 4 Reading/Lecture
Week 4 Reading/Lecture CHEM 2321
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This 9 page Class Notes was uploaded by Hayley Lecker on Friday September 18, 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 55 views. For similar materials see Organic Chemistry I in Chemistry at University of Texas at El Paso.
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Date Created: 09/18/15
Organic Chemistry Week 3 Important Information Professor s Email isalutepedu Class Website organicutepeducourses2324 Class Code Ebook utep232Xfall2015 166 Endo Exo Svn and Anti on Bicvclic Alkanes reference pages 839846 166 The DielsAlder Reaction The DielsAlder Reaction adds an alkene to a conjugated diene to form a cyclic alkene The alkene that reacts with a conjugated diene is called a dienophile This produces a new six membered ring called 42cyclo addition reaction DielsAlder reaction is a concerted reaction in which the diene must achieve the scis conformation before the reaction occurs Transition state far the walla Alder rearsti m The simplest of all DielsAlder reactions is the 13butadiene with ethane proceeds with difficult At 200 C it yields cyclohexene only 20 of the time However substituting a dienophile with a carbonyl produces a cyclohexene 100 Below are example of these two reactions It 1 rr Hf ng game a II M l I Eli1 Each 3 t quot 1 l mum Alkynes make good dienophiles however it reacts poorly unless there is an electronwithdrawing group bonded to the triple bond II I g momma H P HH a f a AmongH3 SHEF Maw 34 DielsAlder reactions are stereospecific the diene must adopt the scis conformation or the reaction doesn twon t take place Positions of the substitutes remain in the relative arrangements meaning if they were cis on the dieneophile they are cis on the product the same with trans quotl CHII El i If REE faggot 1 E l a l E LEIGH 95 DielsAlder reaction is also stereoselective The addition of methyl acrylate to cyclo pentadiene to form a bicyclic system produces endo isomers more than exo isomers C a H r go to H39 27 isomer Exp DielsAlder reactions are kinetically controlled this means they go towards the least amount of energy but this doesn t mean the most stable not thermodynamically it has an equilibrium Endo is slightly lessstable than exo but it requires less energy to form It is more energy to form a more stable isomer because of the orientations of the carbonyl group The major product comes from the transition state where the electron withdrawing groups orient themselves sny with respect to the diene Now you may be confused about endo exo syn and anti Exo and Endo are only used with the methyl is on the two largest bridged Endo looks like As you can see there is a bridge formed when you line the bridgehead together and if the methyl is pointing downward in relation to the cup it is Endo Please note this only applies if the bridgehead s hydrogens are cis Exo ls up in relation to the bridge this again only is true if the bridgehead hydrogens are cis M w Syn and Anti are used when the methyl is on the smallest bridge this is usually on a bridge that is in the middle of the bridgehead Syn means the methyl points to the largest bridge Anti means the methyl points away from the largest bridge Cis and trans are used when the methyl is on the bridgehead Endo Rule Alder Rule As the pi bonds of the electron withdrawing group approach the C2 and C3 atoms of the diene the proximity of the electron withdrawing group to these carbons results in a secondary overlap between orbitals of the carbons and orbitals of the electron withdrawing group The secondary overlap influences the reaction but does not form bonds primary overlap does form a bond n DielsAlder reaction secondary overlap helps to stabilize in the transition state Meet Stable ml39a li gquot H atquot the reactante Zleade tn T title 1mg etabile emin product Citing 3 Meet Stable e entaiem ef the madame leads E 39 ten the tIl IE Stable em HECng Emmanuel H 29210 137 Acyclic Alkenes EZ Nomenclature reference pages 100109 678679 29 Naming Alkenes and Alkynes Alkenes and cycloalkenes are hydrocarbons that have 1 or more carboncarbon double bonds The equation for this is CnHZn Alkenes and cycloalkanes are constitutional or structural isomers Naming Alkenes 1 Find the longest continuous chain containing the double bond this will be the parent chain 2 Replace ane of the parent chain with ene 3 Indicate position of double bond by numbering parent chain to give the double bond the lowest number GHEUHEClIz g CHEGHECIIz39CIIUHS l Ex utene Ei Plentene 1101 Bw Kh t mint 3 pentene Double bonds take priority over substituents Methgril Ei hmtene Example of Naming Alkenes The fellewi hg example ehewe etep lby etepl lhe w tr name an alkene Step 1 the llehgeet chain ef39 ee rhe he eehtaiphlg the leuhlle hand It eehtaipe six anathema 4 a Step 2 Name the parent chain lite name ie heatehe Step 3 Determine the peei e h ef the dmlhle trend in the parent chain In this ease yen number the parent elhej h them right te left lheeauee that gives the rst eefbep ef39 the de hle hand the leweet number The parent name ie EhEIE E 5 3 l V itl r 1 Step 4 Number and meme the ETIJhE 39tllJ tE The E mp d has twe Inethjgrl greppe bended to Step 5 Put tegetlne r all the piecee ef the name The eem peu hdh ee m plete name is g edimethyl E hexe he x lquot 51 414 Eimethy1 E hexe11e Naming eyelleelkehee e similar tit aming elkepeeg except that yen pumlher the ring er that the de hle lhend is between 1 and GE Naming cycloalkenes is similar to alkenes except you number the ring so the double bond is in between C1 and C2 Example below H ff Haw Polyenes contain 2 or more double bonds Dienes contain 2 double bonds and trienes three To Name Dienes or Triene Follow alkene rules plus these addition rules 1 Write numbers indication locations of double bond separated with common then a hyphen 2 After hyphen change parent ending from ene to diene if two triene if three and so forth Example of Naming Dienes or Trienes Step 1 the nn nlhera indicating the leea e ne cf the dnnhle henda eeparated by ce nlrnaa and fellewed by a hyphen Step 2 the hyphen write the parent name if the eenrpeund changing the ending frcrn cnc dicnc if there are twe deuhlle hands er triene if there three etc The fe ewing eaarnple de nte natratee hew ta name a pellpene Step 1 Determine the llength cf the parent chain and the peaitiena cf the denim1e hands The parent chain is Bil carhene lung There are ten dcuhlle hende and their pcaiticne are C1 and 34 5 4 5 3 1 Step 2 the numbers ef the llecaticne cf the cicuhlle henna fellinwed he a hyphen 14 Step the hyphen write the narne cf the parent chain with the niche ending The name if the ccmpeu nd ta 154thiiene l chac cne Special Types of Dienes Conjugated double bonds separated by one single bond CH2CHCHCH2 Chemical properties differ greatly from simple alkenes Cumulated double bonds share a carbon CH2CCH2 A side chain containing a double bond is an alkenyl Naming alkenyl 1 Number carbons from the carbon that bonds the side chain to parent 1 3 139 4 2 When naming side chain use ending eny instead of ene Use parentheses so you know the number belongs to side chain Alkynes are often called acetylenes because of the common name of the simplest compound of this type Ethyne HCECH which common name is acetylene IUPAC Naming of Alkynes 1 Find parent chain must contain the triple bond 2 Add yne to ending instead of ane 3 Number so triple bond has the lowest number 4 Place number of triple bond first then hyphen to parent chain If double bond and triple bond in competition use the above procedure for naming the parent chain then for determining bond position use the following 1 Find longest continuous chain with both triple and double bond 2 Number the chain so multiple bonds get lowest numbers 3 Number position of the double bond to parent CH2CH2CEIECH3 4 Use en are the end of parent name 5 For triple use yne ending along with number identifying position Number double bond so triple takes precedence over substituents If both groups could get the same number en takes priority and gets the lowest number 3CHCHI IQEEECH3 E Helpten sue Her H atenl E jmej CH2 SCH 1 Hexem 4 fsme 210 Naming Alkenes Part II Alkenes do not rotate around double bond so they can have cistrans isomerism H I 39a eek fe ea H lIiIZ H eis Items For complex structures cis or trans refers to the parts of the main carbon chains in which double bond is found squotf mE Methjrl Eheme Sample seiwticm e Te name eempmsl mzi feiiew these step Step 1 Determine the parent chain The lenges t chain that l t j the deuhie bend hes sis esthen stems with the pesitieu ef39 the deuhle hemzi at BB Thus the perth chain is E ihEKEI E Step 2 The substituent is a methyl group in Ed Step 3 The twin auhatituenta attached to the double hand are in opposite sides of the double bond and thus are trans tut each other The name of this mmpo mld is trans 4 methyl 2heztene 137 EZ Nomenclature Z and E is a general system to describe cis and trans relationships The EZ method of naming is based on the CahnIngold Prelog system of substituent priorities To determine whether E or Z assign each group bonded to doubled bonded carbons are priority number Assign groups to the left a 1 and 2 and right 1 and 2 Assign 1 to group with the atom having a higher atomic number 1 HER firm m 3 Haifa EH 2 E C V H H 5 i1 E E Erutteme EE Eutr e d 39g39 um RENEE Hm As you can see in the above image 2 makes a quotboatquot and E looks more like a quotchairquot if you don t look at the hydrogens and just look at the methyls So if 1 groups are on the same side it is Z isomer if 1 groups are on opposite sides it is E isomer 313Monocyclic Alkenes reference pages 165 313 Stereochemistry of Polycyclic Ring Systems Pg 165 only the rest of 313 is covered in week 3 notes Cyclohexene and other small cycloalkenes always have cis double bond The smallest transcycloalkene is transcyclooctene with strain energy of 10kcalmol compared to ciscyclooctene Bredt s Rules a bicyclic compound with a double bond ti bridgehead carbon that is a part of a small ring is unstable This is so unstable no one has isolated it BicycldEZEI 1Q heptene Lecture Notes MethylMethyl elipsing is 41 kcalmol MethylHydrogen elipsing is 12 kcalmol MethylMethyl gausch is 8 kcalmol MethylMethyl anti is 0 kcalmol The following image is an example of axial and equatorial bonds Equatorial bonds are more favored H CH Red 33331 bond Ho HO Blue Equatori 31 bond Ho oH
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