Journal of Molecular Structure, 40 (1977) 1-11
@Elsevier Scientific Publishing Company, Amsterdam
- Printed
in The Netherlands
MICROWAVE SPECTRUM, CONFORMATIONAL PREFERENCE,
INTRAMOLECULAR HYDROGEN BOND, BARRIER TO INTERNAL
ROTATlON, DIPOLE MOMENT, AND CENTRIFUGAL DISTORTION
OF l-FLUORO-2-PROPANOL
K.-M. MARSTOKK and HARALD MØLLENDAL
Department of Chemistry, The University of Oslo, Blindern, Oslo 3 (Norway)
(Received 31 January 1977)
ABSTRACT
The microwave spectra of 1-fluoro-2-propanol,
CH3CH(OH)CH,F,
and one deuterated
species, CH,CH(OD)CH,F,
have been investigated in the 18-30 GHz spectral region.
Only one rotamer with an intramolecular
hydrogen bond forme d between the fluorine
atom and the hydroxyl group was assigned. This conformation
is also characterized
by
having the C-F bond approximately
anti to the methyl group. The FCCO dihedral angle
is 59 :t 2° and the HOCC dihedral angle is 58 :t 3°. Further conformations,
if they exist,
are at least 0.75 kcal mol-' less stable. Five vibrationally
excited states belonging to
four different normal modes were assigned and their fundamental
frequencies
determined.
The barrier to internal rotation of the methyl group was found to be 2796 :t 50 cal mol-' .
The dipole moment is /la = 0.510:t 0.009 D, /lb = 1.496 :t 0.026 D, /le = 0.298 :t 0.014 D,
and /ltot = 1.608 :t 0.030 D. Extensive centrifugal distortion analyses were carried out for
the ground and the first excited state of the heavy-atom torsional mode and accurate
values were determined
for all quartic and two sextic coefficients.
INTRODUCTION
In mono-substituted
propanols, where the hydroxyl group and a protonaccepting gro up are placed on neighbouring carbon atoms, two rotamers with
intramolecular hydrogen bonds may exist. These two typical conformations
are shown in Fig. 1 in the case of 1-fluoro-2-propanol.
Form I has the
methyl group approximately anti to the C-F bond, while conformer Il has
the methyl group roughly in the gauche position. These rotamers are
interchangeable by an approximately 1200 rotation about the CH(OH)-CH2F
bond followed by an appropriate rotation about the C-O bond allowing
the hydrogen bond to be formed. Further rotamers not stabilized by
hydrogen bonding are of course possible, but are expected to be of considerably higher energies. For example, it has very recently been shown by
Hagen and Hedberg [1] that the hydrogen-bonded conformation of the
closely related niolecule 2-fluoroethanol is at least 2.7 kcal mol-1 more
stable than any non-hydrogen-bonded
anti form. The high stability of
2
H
H
H
H
',OH
H
H
HO
,CH3
, , , ,
F"
I
....
"F"
IL
Fig. 1. The two possible intramolecularly
hydrogen-bonded
conformations
of l-fluoro-2propanol viewed aiong the CH,F-CH(OH)CH3
bond. Dots indicate possible nonbonded
stabilizing interactions.
It is seen that rotamer Il might be expected to be stabilized not
only by hydrogen bonding, but by dipole-dipole
interaction
between the methyl group
and the C-F bond as well.
this rotamer has be en corro borated by microwave [2] and IR [3] spectroscopic
studies of the gaseous state and IR [3] and proton magnetic resonance work
[4] on condensed phases.
Besides intramolecular hydrogen bonding, rotamer Il might be expected
to be additionally stabilized by attraction between the methyl group and
the fluorine atom. This interaction might be of the dipole type. In fact,
Hirota [5] found that the corresponding conformation of the closely
related n-propyl fluoride is 0.4 7
:!: 0.31
kcal morI more stable than the
anti form. The latter, of course, corresponds to rotamer I of Fig. 1. Since
n-propyl fluoride and 1-fluoro-2-propanol
are so similar, it was expected
that conformer Il would be preferred. However, the microwave spectrum
clearly reveals that this is not the case. Contrary to expectation, rotamer I
is found to be at least 0.75 kcal morI more stable than form Il.
EXPERIMENT
AL
The title compound was synthesized using the procedure of Bergmann
and Cohen [6]. The sample was purified by gas chromatography
before use.
The deuterated species was made by admitting a small amount of heavy
water to the cell already containing the 1-fluoro-2-propanol.
The microwave
spectrum was studied using a conventional Stark modulated spectrometer.
The cell was cooled with small portions of dry ice, and the temperature is
estimated to have been roughly -40°C. The 18-30 GHz spectral region
was examined.
3
RESULTS
Microwave spectrum and assignment of the ground state
Preliminary rotational constants were computed for rotamers I and Il by
combining structural parameters taken from related compounds. Band
moment calculations [7] indicated that rotamer I should have a dipole
moment of about 1.6 D with a dominating component of roughly 1.4 D
along the b-axis while the hypothetical conformation Il was predicted to
have a dipole moment of about 1.4 D with the largest components of
approximately 1.0 D along the b- and c-axes.
The molecule was found to possess a fairly rich microwave spectrum
dominated by Q-branch transitions. The strongest of these were rapidly
assigned as being b-type belanging to the ground vibrational state of form I.
After same searching, low J b-type R-branch lines were identified by their
Stark effects and a full set of rotational constants could be determined.
Additional transitions were then measured and inc1uded in a first order
Watson [8] centrifugal distortion analysis employing Scf>rensen's program [9].
The improved spectroscopic constants thus obtained were used to predict
the frequencies of further medium and high J/P- and R-branch b-type
transitions which were subsequently measured and inc1uded in the least
squares fitting procedure. In this manner about 230 transitions were
assigned. The maximum value of J was 60. At these high values of J the
rotational energies are sa large that quite weak transitions are observed.
Searches for even higher J transitions were not successful presurnably
because intensities were toa low to make definite assignments.
As high J lines were assigned, it was found that the first order Watson
centrifugal distortion formula was insufficient and sextic distortion
coefficients had to be added. Only HJ and HJK could be determined.
Inc1usion of additional sextic coefficients led to correlations close to the
absolute value of 1 and only marginal improvement of the standard
deviation of the fit.
In addition to the b-type lines, several very weak low J R-brancha-type
tran~itions were assigned. No c-type and no Q-branch a-type lines were
found although their frequencies could be very well predicted. This can
be explained by the faet that both Ila and Ile are quite small, 0.510 D and
0.298 D, respectively, thus producing insufficient intensities.
Table llists 41 selected transitions* and Table 2 shows the speetroscopic
constants derived from 205 transitions used in the least squares procedure.
As shown in Table 2, very accurate values have thus been obtained not
only for the rotational constants but for the centrifugal distortion constants
as well.
*The complete list of frequencies for the ground, the vibrationally
excited states, and
the deuterated speeies is available from the authors upon request, or from the Microwave
Data Center, Molecular Spectroscopy
Section, National Bureau of Standards, Washington
D.C. 20234, U.S.A., where it has been deposited.
4
TABLE 1
Selected
transition
Transition
a-type
20" --+30,3
21" --+3",
41,4 --+5 1,5
b- type
1,,0 --+2,,1
30,3 --+41,4
73,4 --+8,,7
104,6 --+113,9
16.,. --+ 177,,1
16.,9--+ 177,10
2614,12 --+2713,15
2614,13 --+2713,14
321.,14 --+3317,17
321.,15--+
38'1,17
38Z1,I.
46,6,20
46'6,Z1
3317,16
--+39'0,'0
--+39'0,19
--+4715,13
--+47 15,n
5230,22 --+ 5329,25
5230,23 --+5329,'4
5833,25 --+5932".
5833,'6 --+5932,27
1611,S --+151,,4
1611,6 --+151,,3
2315,. --+22'6,7
23,5,9 --+22'6,6
30'9,11 --+29'0,10
30,9,12 --+29,0,9
4025,,5 --+39'6,14
4025,16 --+39'6,13
4730,'7 --+4631,'6
4730,1. --+4631,15
6037,13 -+ 593.,n
6037,,4 --+593.,Z1
70,7--+7.,6
3,,3 --+3,,2
7,,7 --+7,,6
5,,3 --+53"
5,,4 --+53,3
10".
--+ 103,7
113,. -+ 114,7
153,12 --+154,1,
a:!:0.10 MHz.
for the ground vibrational
state of CH3CH(OH)CH,F
Observed
frequencya
(MHz)
Obs.-calc.
frequency
(MHz)
18559.95
20100.36
29138.40
0.01
-0.05
-0.03
-0.06
-0.15
-0.26
0.00
0.00
0.00
28453.99
26767.54
18344.59
29612.59
29551.29
29641.41
28351.62
28351.62
23252.83
23252.83
29559.43
29559.43
26670.27
26670.27
21735.17
21735.17
28077.99
28077.99
22258.97
22258.97
20646.34
20646.34
18994.63
18994.63
19750.73
19750.73
29108.65
29108.65
21113.20
21113.20
22362.54
18775.63
28402.94
25105.25
27842.10
20620.48
30003.4 7
28016.92
0.07
-0.02
0.01
0.05
-0.06
0.06
-0.03
-0.04
0.03
0.03
-0.10
-0.10
0.06
0.06
-0.02
-0.02
-0.09
-0.09
0.08
0.08
0.13
0.13
-0.07
-0.07
-0.08
-0.08
0.11
0.11
-0.14
-0.14
0.03
0.03
0.08
-0.02
0.10
0.03
0.00
-0.07
-0.18
-0.28
1.03
1.87
5.93
5.80
28.84
28.84
56.14
56.14
92.09
92.09
165.87
165.87
242.4 7
242.4 7
331.97
331.97
-7.20
-7.20
-21.50
-21.50
-47.45
-47.45
-111.74
-111.74
-181. 70
-181. 70
-372.13
-372.13
-1.32
-0.33
-1.74
-1.02
-1.22
-3.48
-5.70
-10.25
0.00
0.00
0.00
6.00
0.01
0.01
0.11
0.11
0.23
0.23
0.56
0.56
1.23
1.23
1.92
1.92
3.51
3.51
0.01
0.01
0.02
0.02
0.03
0.03
0.03
0.03
0.24
0.24
-0.41
-0.41
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Centrifugal
Total
(MHz)
distortion
Sextic
(MHz)
BLE 2
ctroscopic
'ational
constants
and CH3CH(OD)CH2F
Grounda
First excited
torsiona
,ber of transitions
.1Hz)
205
0.077
MHz)
MHz)
MHz)
kHz)
8570.5576
:!:0.0043
3566.4735
:!:0.0017
2742.4504
:!:0.0021
0.7646 :!:0.0061
6.416 :!:0.058
1.640 :!:0.020
0.1747 :!:0.0038
3.56 :!:0.11
0.001079
:!:0.000051
-0.0209
:!:0.0011
,
(kHz)
(kHz)
tHz)
kHz)
Hz)
(Hz)
state
for CH3CH(OH)CH2F
Second lo west bending
modea
Ground b
25
0.244
21
0.136
24
0.087
8592.314:!: 0.051
3561.633:!: 0.020
2733.601:!: 0.019
d
8.08 :!:0.88
-11.5:!: 6.0
0.228 :!:0.052
2.96 :!:1.05
d
d
8519.227:!: 0.040
3560.406:!: 0.018
2737.034:!: 0.018
d
7.17 :!:0.47
0.8:!: 3.5
0.264 :!:0.030
2.82:!: 0.59
d
d
8158.248 :!:0.016
3566.051 :!:0.013
2698.411 :!:0.012
0.59 :!:0.25
7.32:!: 0.42
0.15:!: 2.24
0.182 :!:0.020
3.38 :!:0.42
d
d
Lowest
modea
117
0.062
Second excited
heavy-atom
torsiona
31
0.151
8525.0492
:!:0.0056
3561.8778
:!:0.0020
2739.9096
:!:0.0024
0.7825 :!:0.0072
6.326 :!:0.064
1.158:!: 0.025
0.1714 :!:0.0059
3.51 :!:0.12
0.00147 :!:0.00019
-0.0144
:!:0.0037
8485.663 :!:0.029
3557.479 :!:0.011
2737.203 :!:0.012
0.85:!: 0.11
6.25:!: 0.39
1.3 :!:2.6
0.197 :!:0.024
2.80 :!:0.48
d
d
:ertainties represent one standard deviation.
13CH(OH)CH2F. bCH,CH(OD)CH2F.
CStandard
heavy-atom
deviation
of the fit. dNot
determined.
bending
Assumed
to be zero.
<:J1
6
The deuterated species, CH3CH(OD)CHzF, was studied mainly to obtain
structural information on the intramolecular hydrogen bond. The assignment
of its ground vibrational state microwave spectrum was made quite readily.
In this case 24 transitions involving J less than 16 were measured. The
resulting spectroscopic constants are displayed in Table 2.
Vibrationally excited states
The ground state lines were accompanied by a rich satellite spectrum
presumably belonging to vibrationally excited states. Five of these were
ultimately assigned to four different normal modes as shown in Tables 2
and 3. The strongest satellite spectrum was assigned to the first excited
state of the heavy-atom torsional mode. Relative intens it y measurements
[10] yielded 109 :t 10 cm-1 for its fundamental frequency. As shown in
Table 2, about 120 transitions of b-type were assigned to this made
yielding high-accuracy spectroscopic constants. The maximum value of J
was 43 in this case and, as in the case of the ground state, the sextic
coefficients HJ and HJK were determined.
The sec ond eJ~cited state of this mode was also assigned, and the derived
spectroscopic constants are collected in Table 2. The variation of the
rotational constants upon excitation of the heavy-atom torsional mode is
seen to be quite linear. It is therefore concluded that this mode is nearly
harmonic [11].
Table 2 includes the spectroscopic constants of what is believed to be the
lowest bending mode. The centrifugal distortion constants were not well
characterized in this case and so few R-branch lines were measured that
I::.Jcould not be determined at all. Relative intens it y measurements
yielded 151 :t 15 cm-l for this fundamental.
Twenty-one lines of the first excited state of the presumed second
lowest bending fundamental were assigned. The derived spectroscopic
constants are listed in Table 2. The remarks made for the preceding mode
with regard to the centrifugal distortion coefficients are valid in this case as well.
TABLE 3
Molecular constants
CH,CH(OH)CH,F
Rotational constantsa
A = 8555.31 :t 0.07
AA
AE
= 8555.13
:t
= 8555.40:!:
Direction
for the first excited
(MHz)
B
0.05
BA
0.05
AE
state of the methyl
group torsional
= 3563.57
:t
0.07
c
= 2740.37
= 3563.71
:t
0.05
:!:
0.05
CA
CE
= 2740.49
= 2740.31
= 3563.50
:!:
:!:
:t
cosines
Aa = 0.8544
Ab = 0.4641
Ac = 0.2336
Barrier, reduced barrier, and moment of inertia of methyl top
V, = 2796:!: 50 cal mol-'
s = 78.78
la. = 3.20 uA'
a Uncertainties
of rotational
constants
represent
one standard
deviation.
0.06
0.04
0.04
mode of
7
Moreover, about 20 transitions attributable to the first excited state of
the methyl group torsional mode were measured and will be discussed below
in the section on barrier determination.
Barrier to internat rotation of the methyt group
Most of the Q-branch transitions belonging to the first excited state of
the torsional mode of the methyl group display ed typical splittings due to
tunnelling through the three-fold barrier. The splittings of the R-branch
lines were generally less than in the case of the Q-branch transitions and
could not be resolved. Both the A- as well as the E-species lines could be
fitted reasonably well to Watson's first order centrifugal distortion formula
using the same unresolved R-branch transition. The resulting rotational
constants are given in Table 3. The centrifugal distortion constants obtained
were so inaccurate that they are not quoted in this Table.
The Q-branch lines of Table 4 were used to determine the rotational
barrier since they display well-defined splittings. Our computer program
described in ref. 12 was used to calculate the barrier. The direction cosines
of the methyl group quoted in Table 3 were computed from the plausible
molecular structure shown in Table 5. The moment of inertia of the methyl
group about its symmetry axis was assumed to be 3.20 uA2. V3 was then
varied to match the observed splittings exactly with the results shown in
Table 4. The average barrier was found to be 2796 cal mol-I. The error
limit is difficult to estimate, but :1:50 cal mori seems reasonable when
taking into account possible systematic errors. A torsional frequency of
208 cm-I is calculated from the barrier. This alm ost coincides with
210:!: 15 cm-I determined by the relative intensity method.
TABLE 4
Split Q-branch lines of the first excited
to determine the rotational barrier
Transitions
Observed
VA
9.,8 -> 9,,7
82,6 -> 83,s
92,7 -> 93,6
102,8 -> 103,7
112,9 -> 113,8
132,1, -> 133,,0
62,s -> 63,.
113,8 -> 11.,7
123,9 -> 12.,8
133,10 -> 13.,9
143,,1 -> 144,10
a
20888.70
21091.15
20422.44
20577.06
21753.02
27532.38
28545.65
29915.29
28195.60
27104.12
26956.78
state of the methyl
frequencies
vA
(MHz)
-
VEb
-0.50
-1.62
-1.53
-1.16
-0.98
-0.45
-1.90
-2.49
-2.13
-1.96
-1.49
MI-h'
b+fIl
(\ l\"T-J~
Barrier
(cal mol-')
2800
2780
2761
2803
2784
2827
2755
2793
2816
2807
2835
Average
a+fIl1;
group torsional
2796
mode used
8
T ABLE 5
Plausible structural parametersa
rotamer I of CH,CH(OH)CH2F
Assumed struetural
C-F
C-O
FH,C-CH(OH)-(HO)HC-CH,
o-H
C-H
and observed
parameters
1.379 A
1.427 A
1.533 A
1.520 A
0.990 A
1.093 A
and calculated
LFCC
LCOH
LCCC
LCCH
LHCH
LHCO
L FCCCdihedral
Fitted
struetural
LFCOOdihedral
LHOCCdihedral
Kraitehman
Observed:
Calculated:
Ao
Bo
Co
constants
of
109.50°
105.00°
112.00°
109.48°
109.48°
109.48°
180.00°
parameters
= 59
= 58
:t 2° from
:t 30 from
syn
syn
's eoordinates for the hydroxyl
lal
Ibl
0.1464 A
1. 7338 A
0.2856 A
1.7338 A
Hydrogen bond parameters
H. . . F
2.351 A
LC-F,OHb
5.72°
Rotational
rotational
eonstants
Observed
8570.5576
3566.4 735
2742.4504
O...F
LOH. . . F
hydrogen atom
lei
Imaginary
0.1142 A
2.783 A
105.43°
(MHz)
aSee text; bangle between
Calculated
8550.02
3552.66
2731.63
C-F
and o-H
Difference
0.24%
0.39%
0.39%
bonds.
The anti form of ethanol has the CH3CH(OH)-fragment in common with,
and the hydroxyl gro up conformation similar to, that of 1-fluoro-2-propanol.
In anti ethanol the rotational barrier is 3329 :t 25 cal mol-I [13]. The
barrier is thus aremarkable 533 cal mol-I less than in anti ethanol. However,
the barrier is dose to 2.69 kcal mori which Hirota [5] determined for
anti n-propyl fluoride. In another related molecule, 1-amino-2-propanol
[14],
the rotational barrier was found as 3173 :t 100 cal mol-I, which is doser to
the ethanol case than to the title compound. The fluorine atom thus has a
large effect on the bar rier height in the two propane derivatives. We find
this noteworthy since the fluorine is not bonded to the atom to which the
methyl group is attached.
Searches for further conformations
The assignments made as described above indude a total of about 450
transitions for the parent species and encompass all strong and practically
all medium intensity lines of the spectrum. A large fraction of the weak
transitions was also accounted for.
9
In an attempt to assign further rotamers careful Stark effect studies were
made among the remaining weak lines, but no Stark splitting could be
resolved. A restricted version of van Eijck's assignment procedure [15] was
then employed. In particular, thousands of possibilities were teste d for
transitions that might belong to the expected relatively strong b- and c-type
Q-branch of the hypothetical rotamer Il. However, these efforts were
unsuccessful. It is felt that additional rotamers would have been discovered
if their individual concentrations had exceeded 10-15% of the total.
Rotamer I is thus conservatively estimated to be at least 0.75 kcal mol-l
more stable than any other conformation of the molecule.
Structure
Only six moments of inertia were determined for conformation I shown
in Fig. 2. Consequently, a full molecular structure cannot be determined.
Instead, we restricted ourselves to fitting the dihedral angles FCCO and
HOCC with the rest of the structural parameters selected from related
molecules as indicated in Table 5. The FCCO dihedral angle was fitted by
minimizing the sum of the absolute values of the per cent differences
between the observed and calculated rotational constants. In this manner
a dihedral FCCO angle of 59 :!: 2° from the syn position was found. The
HOCC dihedral angle was found by the following procedure. The principal
axes coordinates of the hydroxyl hydrogen were first calculated by
Kraitchman's equations [16] as lal = 0.1464 Å, Ibl = 1.7338 Å, and with
the c-coordinate found to be imaginary . The a-axis coordinate is so small
that no reliable value for the dihedral angle can be found by fitting to this
parameter. Fortunately, the b-coordinate is large and the HOCC dihedral
angle was then determined by fitting this angle until the b-coordinate was
Fig. 2. Model of conformation
I of l-fluoro-2-propanol.
10
reproduced exactly. This yielded 58 :t 3° from the sy n position for this
angle. In 2-fluoroethanol the FCCO dihedral angle has be en determined as
62°12' :t 1° by microwave spectroscopy [2] and as 64.6 :t 1.1° byelectron
diffraction [1], while the HOCC dihedral angle was found to be 55°33' :t 3°
[2]. These values are thus dose to their counterparts in 1-fluoro-2-propanol.
Table 5 als o summarizes important parameters characterizing the intramolecular hydrogen bond. The OH. . . F distance is seen to be about 2.35 Å
which is 0.2 Å shorter than the sum of the van der Waals' radii of fluorine
and hydrogen [17]. The C-F and O-H bonds are approximately 6° from
bein g parallel. This would lead to a very favourable electrostatic interaction
if the popular molecular model which assumes that localized bond dipoles
exist within molecules were correct [2, 18]. Moreover , the hydrogen bond
is very far from being linear with the O-H, . . F angle of about 105°. This, of
course, implies that conditions for covalent bonding are rather unfavourable.
The great stability [1-4] enjoyed by the hydrogen-bonded conformations
in this sort of molecule thus seems perhaps to be largelya result of
favourable electrostatic conditions rather than covalent forces in the
hydrogen bond formation.
Dipole moment
Stark coefficients of the 62.5 -7 63,4 and 91,8 -7 9L,7transitions were used to
determine the dipole moment. A DC voltage was applied between the
Stark septum and the cell with the modulating square wave voltage
superimposed. The DC voltage was calibrated employing the OCS 1 -7 2
transition
with /locs
= 0.71521
D [19].
The second
order coefficients
are
given in Table 6. A least-squares fit utilizing a diagonal weight matrix
was performed. The weights were chosen as the inverse squares of the
experimental standard deviations of the coefficients appearing in Table 6.
The results were /la "=0.510 :t 0.09 D, /lb = 1.496 :t 0.026 D, and
/lc
= 0.298 :t 0.014 D with a total dipole moment of 1.608 :t 0.030 D. As
expected, this is only slightly larger than that of 2-fluoroethanol.
(1.51:t 0.02 D [2]).
DISCUSSION
Not unexpectedly, an intramolecular hydrogen bond was found to be
present in the most stable conformation of the molecule. However, the
reason why rotamer I is preferred to the hypothetical form Il is difficult
to find, as this is a situation opposite to that of n-propyl fluoride [5].
Steric repulsion between the fluorine atom and the nearest of the methyl
group hydrogen atoms is hardly the cause, since there is little reason for
believing that there could be rather large geometrical differences between
gauche n-propyl fluoride and the hypothetical rotamer Il of 1-fluoro-2propanol. In fact, we think that the present example once more shows how
complicated barrier forces may be and how limited simple mo dels of ten
11
T ABLE 6
Stark coefficients
and dipole moment
Transition
of CH3CH(OH)CH2F
fl v/E 2 (MHzV-2 cm2)'10.
Obs.
= 0.510
-19.70
IMI = 7
IMI = 8
IMI = 9
9.,8 -->92,7
Ila
4.38 :t 0.04
-9.50:t
0.09
IMI = 3
IMI = 5
IMI = 6
62,5 --> 63,4
:t
Calc.
:t
0.20
4.21 :t 0.04
5.56 :t 0.05
7.01 :t 0.07
4.376
-9.623
-19.249
4.507
5.335
6.812
0.009 D, Ilb = 1.496 :t 0.026 D, Ile = 0.298 :t 0.014 D, Iltot = 1.608 :t 0.030 D
Uncertainties
represent
one standard
deviation.
are for.making predictions. Clearly, the popular model which assumes that
potential functions are transferable [20] between related molecules would
have failed in this case although it may be quite successful for other examples.
ACKNOWLEDGEMENTS
The authors are grateful to Cand. Mag. Arne MØller and his supervisor
Cand. Real. Leiv Kr. Sydnes for synthesis and to Miss Gerd Teien for gas
chromatography of the sample used in this work.
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