Chapter04

Chapter04 - 4.17. Synthesis of Alkanes and Cycloalkanes...

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Unformatted text preview: 4.17. Synthesis of Alkanes and Cycloalkanes Hydrogenation: H2 alkene alkyne Chapter 4 - 1 alkane Chapter 4 - 2 ? CO2Me CO2Me Ans) H2, Ni (or Pd), EtOH H2, Pd O Ans) Not formed ? O O Synthesis: Alkylation of Terminal Alkynes Chapter 4 - 3 Question) Complete the following reaction by giving conditions and the appropriate intermedite. R H R R' Answer) Question) Synthesize the following multistep synthesis. Answer) Chapter 4 - 4 Chapter 4. Nomenclature and Conformations of Alkanes & Cycloalkanes 4.3. IUPAC Nomenclature See Table 4.3 for The Unbranched Alkanes: Methane, ethane, propane, butane, pentane, hexane, heptane, octane, Nonane, decane, undecane, dodecane, tridecane, - - - - - - Nomenclature (Naming) 1. Longest continuous chain: parent name (-----alkane) incorrect 6 C's both same correct hexane heptane 7 C's 2. Numbering: Start near the substituent (Substituent at the lowest possible number) 6 5 4 3 2 1 correct 1 2 3 4 5 6 incorrect incorrect 1 2 3 4 5 6 5 46 3 7 1 correct 2 7 9 8 7 6 5 4 2 nonane Chapter 4 - 5 Q) Identify the parent chain and number carbons. answer 3 1 3. Name: #-sub-alkane (or #-alkylalkane) 6 5 4 3 2 1 7 methyl 2-methylhexane 6 5 4 2 3 1 methyl 3-methylheptane Chapter 4 - 6 4. More sub: #1-sub1-#2-sub2-alkane (or #1-alkyl-#2-alkylalkane) Note: sub1 & sub2 in alphabetical order methyl 1 methyl 2 3 1 4 5 6 ethyl ethyl 2 4 6 ethyl > methyl 4-ethyl-2-methylhexane ethyl > methyl 3 5 5. Sub on the same carbon: #1 = #2 3-ethyl-3-methylhexane 6. Identical sub: sub1 = sub2 #1,#2-di-sub-alkane (#1,#2-dialkylalkane) #1,#2,#3-tri-sub-alkane; #1,#2,#3,#4-tetra-sub-alkane methyl 3 1 methyl 2 4 2,3-dimethylbutane butane di, tri, etc are not counted for alphabetical order Chapter 4 - 7 7. More sub: Two longest chains for possible parent ---> Pick the one with more substituents 4 7 6 5 3 3 2 1 2 Two substituents 1 2,3,5-trimethyl-4-propylheptane No substituent 8. sub: at the lowest possible number (also at the first point of difference) correct: 2,3,5-trimethylhexane 5 4 3 2 1 1 3 45 2 6 6 3 is lower than 4 incorrect: 2,4,5-trimethylhexane Chapter 4 - 8 4.3C. Branched alkyl groups Numbering begins at the carbon attached to the parent chain. 1-methylpropyl (sec-butyl) 2 1 3 1,1-dimethylethyl (tert-butyl) 2 2 1 3 sec and tert are not considered for alphabetical order. They show structures, and not part of names. 1 2 1 1-methylethyl (isopropyl) 2 3 propyl 1 2 3 2-methylpropyl (isobutyl) 1 3 2,2-dimethylpropyl (neopentyl) 2 iso and neo are considered for alphabetical order. They are part of names. Q) Name the compound. 8 7 6 9 answer 5 4 2 3 1 5-ethyl-6-isopropyl-2,3,4,7tetramethylnonane 5-ethyl-2,3,4,7-tetramethyl-6-(1methylethyl)nonane Chapter 4 - 9 Q) Draw the structure for the following name. 5-sec-butyl-2,3,8-trimethylnonane = 2,3,8-trimethyl-5-(1-methylpropyl)nonane Ans) 8 5 2 3 4.3E. Alkyl halides: haloalkane Br Cl Chloroethane 3 2 F 1 1-fluoropropane 3 2 2-bromopropane 1 1. Sub: lowest number regardless of halo or alkyl Cl 1 2 3 4 5 1 2 3 4 5 2-chloro-3-methylpentane Cl 3-chloro-2-methylpentane Chapter 4 - 10 2. If two sub at the same #, number them in alphabetical order. Cl 1 2 3 4 5 2-chloro-4-methylpentane 5 Cl 4 3 2 1 incorrect 4.3F. Alcohols: #-alkanol 1. Find the chains containing OH. HO OH 2-butanol parent chain due to the OH present Not a parent chain even if the longest chain 2. Choose the longest one ---> parent chain HO parent chain due to longer nonanol not a parent chain due to shorter Chapter 4 - 11 3. Numbering: the lowest # for OH, not for other sub any more HO 9 8 7 6 5 4 3 1 2 8 7 6 5 4 3 2 1 OH 7-methyl-3-octanol 3-propyl-2-nonanol 4. Two alcohols ---> diol: #1,#2-alkanediol HO 3 4 5 1 Cl 2 OH 7 6 HO 8 9 (For your own practice) 6-sec-butyl-5-chloro-3,8-dimethyl-2,7-nonanediol 4.4. Cycloalkanes 4.4A. Monocyclic Compounds cycloalkane parent chain isopropylcyclohexane No need to # Chapter 4 - 12 Consider the lowest # & sub in alphabetical order methyl 5 4 3 2 1 1 isopropyl higher priority over "methyl" 3 2 # starts at here 1-isopropyl-3-methylcyclohexane When three or more sub, the lowest set of locants 4 13 2 1 4 Cl 1,2,4 is better than 1,3,4. 4-chloro-2-ethyl-1-methylcyclohexane Cycloalkyl can be used as a sub, similarly to alkyl Efavirenz (DMP-266), HIV drug cyclopropylacetylene Chapter 4 - 13 4.4B. Bicyclic compounds Bridged rings bridgehead Fused rings bridgehead bridge In both cases, bicycloalkane as the parent chain 2 C's 2 C's 1C 1. Total # of C's: bicycloheptane 2. # of C's in the bridges in the decreasing order: [2.2.1] -----> bicyclo[2.2.1]heptane How about? bicyclo[3.2.1]octane Chapter 4 - 14 3. Numbering: a. starting at one bridgehead b. move along the longest bridge c. move to the next, then the shortest bridge 7 6 1 8 5 4 2 3 7 6 1 8 5 2 3 4 8-methylbicyclo[3.2.1]octane 4. # the sub. If possible, keep # of sub lowest. 5. Fused rings: consider one bridgehead has zero bridge. 9 8 7 1 6 2 This bridge has zero carbon. 3 4 5 8-methylbicyclo[4.3.0]nonane 4.5. Alkenes and Cycloalkenes Chapter 4 - 15 1. The longest chain containing the double bond: parent chain 2. Number the carbon beginning at the end of the chain nearer the double bond. 5 1 4 2 5 3 1 2 3 4 correct incorrect 2-pentene meaning that the double bond is between C-2 and C-3 3. Name sub: the same as before. 1 4 2 3 5 6 4 3 Cl 2 1 2,5-dimethyl-2-hexene 1-chloro-2-butene 4. Cycloalkene: double bond at C-1 and C-2. 5. Cycloalkene: Name sub as before. Correct 6 5 Incorrect 3 Chapter 4 - 16 1 2 3 4 1,5-dimethylcyclohexene lower number No need to put "1-" because it is supposed to be at C-1 and C-2. 2 1 4 5 6 2,4-dimethylcyclohexene higher number 6. Alcohols always prior to alkenes and alkynes. OH 3 1 4-methyl-3-penten-2-ol 5 4 2 6 HO 1 2 3 4 5 2-methyl-2-cyclohexen-1-ol 7. Use cis or trans if known. Cl's are on the opposite sides 9 7 8 6 Cl 5 3 2 1 trans-4,5-dichloro-4-nonen-2-ol Cl's are on the opposite sides 4 OH Cl 4.6. Alkynes: similar to alkenes Chapter 4 - 17 1. The longest chain containing the triple bond: parent chain 2. Number the chain w/the triple bond carbons at the lowest #. 2 8 7 6 5 4 3 1 5-ethyl-7-methyl-3-octyne When there are two or more groups in competition, parent chains can be confusing to decide on. Priority in deciding on the parent chain. alcohol > alkene ~ alkyne > alkane Naming order: -alkyl-alken-yn(e)-ol If alkene & alkyne are at the same #, choose alkene. 1 2 3 4 5 6 7 trans-2-octen-6-yne 8 Chapter 4 - 18 If alkene and alkyne are not at the same #, choose the lowest # for any multiple bond. 3 Cl 1 2 1-chloro-cis-6-nonen-2-yne 4 5 6 7 8 9 Cl 1 2 8 4 5 6 7 9 3 1-chloro-trans-2-nonen-6-yne 4.7. Physical properties of alkanes and cycloalkanes 1. Insoluble in water 2. Less dense than water 3. The more carbons, the higher boiling point 4.8. 4.9. Sigma Bonds and Rotation Ethane has relatively free rotation around the carbon-carbon bond The staggered conformation has C-H bonds on adjacent carbons as far apart from each other as possible The drawing to the right is called a Newman projection Chapter 4 - 19 The eclipsed conformation has all C-H bonds on adjacent carbons directly on top of each other The potential energy diagram of the conformations of ethane shows that the staggered conformation is more stable than eclipsed by 12 kJ mol-1 Chapter 4 - 20 Chapter 4 - 21 staggered staggered (when there are different sizes of substituents) some repulsion gauche anti No repulsion somewhat stable most stable rotate rotate bad repulsion eclipsed unstable torsional strain Chapter 4 - 22 Conformational Analysis of Butane - Rotation around C2-C3 of butane gives six important conformations. - The gauche is less stable than the anti by 3.8 kJ mol-1 (repulsive van der Waals forces between the two methyls) 4.11. Ring strain due to angle strain & torsional strain Chapter 4 - 23 Angle strain is caused by bond angles different from 109.5o Torsional strain is caused by eclipsing C-H bonds on adjacent carbons Cyclopropane has both high angle and torsional strain Bond angle: 60 eclipsed Chapter 4 - 24 Cyclobutane has considerable angle strain It bends to relieve some torsional strain Cyclopentane has little angle strain in the planar form but bends to relieve some torsional strain Cyclobutane: Angle strain No torsional strain Cyclopentane: No angle strain No torsional strain 4.12. Conformations of cyclohexane Chair conformation: no ring strain C-H bonds: staggered Chapter 4 - 25 Boat conformation: less stable; due to flagpole interaction torsional strain 4.13. Axial & Equatorial Chapter 4 - 26 parallel or on the same line ring flip axial equatorial When vertex is up, axial is up. When vertex is down, axial is down. equatorial is parallel to the second bonds in cyclohexane Chapter 4 - 27 Question) Which form of methylcyclohexane is more stable? Ans) Chair form with the methyl in the equatorial. Why?) An axial methyl has an unfavorable 1,3-diaxial interaction with axial C-H bonds 2 carbons away Chapter 4 - 28 Question) Which form of t-butylcyclohexane is more stable? Ans) Chair form with the t-butyl in the equatorial. Only equatorial is observed due to significant 1,3-diaxial interaction between H's and t-butyl. severe 1,3-diaxial interaction H H ring flip H H H Not exist H exclusive 4.14. Cis-Trans Isomerism Disubstituted cycloalkanes can exist as pairs of cis-trans isomers. Cis: groups on the same side of ring Trans: groups on the opposite side of ring Chapter 4 - 29 Chapter 4 - 30 Trans-1,4-dimethylcylohexane prefers a trans-diequatorial conformation Cis-1,4-dimethylcylohexane prefers exists in an axial-equatorial conformation Chapter 4 - 31 A very large tert-butyl group is required to be in the more stable equatorial position Chapter 4 - 32 Assignment: Always solve review problems first. Exercises 4.22 - 4.28 except 4.27 (b) Problems 4.29, 4.30, 4.33, 4.34, 4.35, 4.38, 4.40, 4.41, 4.44, 4.46, 4.47(a), (b) Challenge Problems None ...
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This note was uploaded on 07/13/2009 for the course CHEM 322AL taught by Professor Jung during the Fall '07 term at USC.

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