1. Chapter 2
Strain and Stability

2. 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

3. 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

4. Group Increments

5. 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

6. 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

7. 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

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

9. Conformational Analysis-Ethane

10. Conformational Analysis-Butane

11. g+g– Pentane Interaction

12. Cycloalkane Conformations (3-5)

13. Cyclohexane Conformations

14. 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
CH(CH3)2
2.21 Cl
C(CH3)3 Br
CF3 I
Si(CH3)3
2.5 OH
C6H5
2.8
OCH3
C6H11
2.2
NH2
CH=CH2
N(CH3)2
COCH3

15. 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

16. Transannular Strain in Cyclodecane

17. Polycyclic Systems

18. trans-Cycloalkenes
trans-cyclooctene
trans-cycloheptane

19. Bicyclooctenes

20. 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

21. 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