Computational Chemistry

The accuracy of AM1 and PM3 then, is quite good for bond lengths and angles,
but fairly approximate for dihedrals. The largest error (Table6.1) in bond lengths is
0.065 A ̊(AM1 for MeSH) and in bond angles 7.1(AM1 for HOF). The largest

Cs

O

H 103.6 107.7 H

103.9

(104.5)

C2v

AM1

PM3

Experiment

0.961

0.951

0.969

(0.958)

MP2(fc) / 6-31G*

H C N

1.069

1.071

1.069

(1.065)

1.160

1.156

1.177

(1.153) Civ

1.482

1.469

(1.452)

O O

H

H

0.945

0.976

(0.965) 104.496.5

98.6

(100.0)

C 2

1.310

0.981 C2h for PM3 H

H

H

H

H H

123.4

124.5

(124.3)

1.328

1.338

(1.318)

1.480

1.499

(1.501)

1.331 1.474

124.3

C2v

H

H

H

H

H H

1.507

1.512

1.526

(1.526)

H H

111.8

111.7

112.3

(112.4)

104.5

106.3

(107.2)

O

H

H

H

H

0.949

0.970

(0.963)

1.097

1.097

(1.094)

1.094

1.090

(1.094)

107.5

107.4

(108.0)

Cs

1.119

1.119

107.2

0.964

105.1

1.410

1.395

1.425

(1.421)

H C2v

H

H

H

H H

O

115.4

116.5

(117.2)

1.216

1.228

(1.222)

1.505

1.513

(1.507)

1.235 1.496

115.4

O

H H

1.202

1.221

(1.208)

1.092

1.104

(1.116)

116.4

115.6

(116.5)

C2v

1.111 1.227

115.5

D3d

H

H

H

H

HH

1.504

1.526

(1.531)

1.098

1.093

107.2 (1.096)

107.7

(107.8)

108.2

1.117

1.500

F

H

H

H

1.351

1.392

(1.383)

1.092

1.092

(1.100)

110.3

109.8

(110.6)

C3v

109.5 1.375

1.121

H

H

H

H

113.8 116.6 D2h

(117.8)

1.086

1.085

(1.085)

1.322

1.337

(1.339)

1.098

114.6

1.326

H 104.6 Cs

102.6

(102.5)

0.947

0.979

(0.975)

1.708

1.717

O (1.690)

Cl

0.961 1.733

101.0

S

H H

1.290

1.340

(1.336)

93.3

93.3

(92.1)

95.5 C 2 v

1.323

H

H

H

H

1.801

1.816

(1.819)

1.306

1.341

(1.336)

1.321

1.095

1.090

(1.091)

1.097

1.091

(1.091)

100.0

96.8

(96.5)

S

99.6

1.112

1.115

1.754

H

O

99.4 F

97.2

(96.8)

0.946

0.979

(0.966)

1.396

1.445

(1.442)

Cs

0.971 1.367

103.9

HHDih

1.064

1.066

(1.061)

1.190

1.218

(1.203)

1.061

1.195

1.101

1.100

(1.099)

1.098

1.092

(1.099)

1.469

1.465

(1.471)

0.999

1.018

(1.010)

114.7

115.4

(113.9)

Cs

Cs

1.122

1.000

1.126

1.432

114.3

N

H

H

H H H

C3v

H

H

H

H

1.192

1.220

(1.206)

1.427

1.197

1.433

1.463

(1.459)

H

H

H

1.765

1.779

(1.781)

109.0

110.0

(110.0

C3v

110.6 Cl

1.111

1.741

1.094

1.089

(1.096)

1.491

S

Me O

Me

1.818

1.809

(1.799)

1.557

1.512

(1.485)

104.5

107.4

(106.7)

99.4

95.8

(96.6)

Cs

1.739

105.7

99.7

Fig. 6.2 A comparison of some AM1, PM3, MP2(fc)/6–31G* and experimental geometries.
Calculations are by the author and experimental geometries are from reference [ 107 ]. Note that
all CH bonds are ca. 1 A ̊, all other bonds range from ca. 1.2 to 1.8 A ̊, and all bond angles (except
for linear molecules) are ca. 90 to 120

414 6 Semiempirical Calculations