Chapter 2 Strain and Stability

BDE HCC-H 132 H2C=CH-H 110 CH3CH2-H 98.2 (CH3)3C-H 93.2 (CH3)2CH-H 95.1 CH3CH2-H 98.2 H3C-H 105.1 71.1 82.3 94.5 HCCH 230.7 H2C=CH2 174.1 H3C-CH3 90.4 CH3-NH2 84.9 CH3-OH 92.3 CH3-I 57.2 CH3-Br 70.9 CH3-Cl 84.6 CH3-F 109.9

Heats of Formation for Alkanes ∆Hfo ∆∆Hfo CH3CH3 -20.24 CH3CH2CH3 -24.84 4.6 CH3(CH2)2CH3 -30.15 5.31 CH3(CH2)3CH3 -35.00 4.85 CH3(CH2)4CH3 -39.96 4.96 CH3(CH2)5CH3 -44.89 4.93 CH3(CH2)6CH3 -49.81 4.92

Group Increments

Strain Energy in Cycloalkanes ∆Hfo (calc) ∆Hfo (exp) ∆∆Hfo -29.6 -29.9 0.3 -24.7 -18.3 6.4 -19.7 +6.7 26.4 -14.8 +12.7 27.5

Radical Stability (CH3)3C-H 93.2 (CH3)2CH-H 95.1 CH3CH2-H 98.2 H3C-H 105.1 HCC-H 132 H2C=CH-H 110 CH3CH2-H 98.2

Carbocation Stability (CH3)3C+ 231 (CH3)2CH+ 246 CH3CH2+ 273 +CH3 312 287 H2C=CH+ CH3CH2+ 273 NCCH2+ 318 FCH2+ 290 HOCH2+ 243 H2NCH2+ 218

Carbanion Stability CH3CH2-H 50 (CH3)3C-H 71 H2C=CH-H 44 HCC-H 24

Conformational Analysis-Ethane

Conformational Analysis-Butane

g+g– Pentane Interaction

Cycloalkane Conformations (3-5)

Cyclohexane Conformations

A Values Group A Value H CH3 1.74 D 0.006 C2H5 1.79 F 0.25-0.42 CH3 1.74 D 0.006 C2H5 1.79 F 0.25-0.42 CH(CH3)2 2.21 Cl 0.53-0.64 C(CH3)3 4.7-4.9 Br 0.48-0.67 CF3 2.4-2.5 I 0.47-0.61 Si(CH3)3 2.5 OH 0.60-1.04 C6H5 2.8 OCH3 0.55-0.75 C6H11 2.2 NH2 1.23-1.70 CH=CH2 1.5-1.7 N(CH3)2 1.5-2.1 COCH3 1.0-1.5

Cycloalkanes (CnH2n) Strain Energies Strain Energy 3 27.5 10 12.4 4 26.3 11 11.3 5 6.2 12 4.1 6 0.1 13 5.2 7 14 1.9 8 9.7 15 9 12.6 16 2.0 Medium Rings Small Ring Common Rings Large Rings

Transannular Strain in Cyclodecane

Polycyclic Systems

trans-Cycloalkenes trans-cyclooctene trans-cycloheptane

Bicyclooctenes

A values in heterocycles Group Me 1.8 2.9 4.0 0.8 1.0 i-Pr 2.1 4.2 0.7 1.5 t-Bu >4.5 1.4 >2.7

Donor-Acceptor Ability lone pair > bonding pair C:– > N: > O: (p) > O: (sp2) > F: I: > Br: > Cl: > F: C-H > N-H > O-H > F-H C-I > C-Br > C-Cl > C-F C-S > C-C > C-N > C-O > C-F Acceptor C-F > C-O > C-N > C-C C-I > C-Br > C-Cl > C-F C-S > C-O C-P > C-N