AH

BH

i n tV

(1) (2)

int2

V VV

R R

A bC C

R

2angular partA bC

R

3angular partA B

R

4angular partA BQ

R

2

6

1angular part

2A BC

R

1.93 A

1.97 Å

1.82 Å

H-O=C angle

H-O=C-C

dihedral angle

80 100 120 140 160 180

0

20

40

60

80

C=O...H bond angle (degrees)

C-C

=O

...H

dih

ed

ral an

gle

(de

gre

es)

0.1

1.8

3.4

5.1

6.7

8.4

10.0

electronic energy

(kcal/mol)

acetone-MeOH complex

M05-2X/6-311+g(d,p)

separated reactants:

+7.4 kcal/mol

global min.: -0.11 kcal

angle: 115.7°

dihedral: 4.4°

100 110 120 130 140 150 160 170 180

0

20

40

60

80

C=O-B angle (degrees)

C-C

=O

-B d

ihe

dra

l a

ng

le (

de

gre

es)

0.1

1.8

3.4

5.1

6.7

8.4

10.0

acetone-BF3 complex

M05-2X/6-311+g(d,p)

electronic energy

(kcal/mol)

separated reactants:

+17.4 kcal/mol

global min.:

-0.4 kcal/mol

angle: 124.3°

dihedral: 0.3°

1.61 A

0 10 20 30 40 50

0

20

40

60

80

100

120

140

160

180

the

bin

din

g e

ne

rgy o

f th

e c

om

ple

x (

kca

l/m

ol)

NBO's estimate of the charge transfer energy (kcal/mol)

y = 3.6x - 13

R = 0.93

2.36 Å

2.80 A

2.44 A

2.47 A

favored TS: NCIPlot

Dr. Alan Hyde

- neither the NBO or AIM-based NCIPlot methods

show the putative formyl C-H…O hydrogen bond

disfavored TS: NCIPlot

Dr. Alan Hyde

-it’s still unclear why there’s an energy difference between the

favored and disfavored transition states

-note: calculations were done with B3LYP, which doesn’t

understand pp stacking or other dispersive interactions

-nonetheless, formyl C-H bonds are probably real, but weak

contacts