Journal of Molecular Structure
Elsevier Publishing Company, Amsterdam
- Printed
in the Netherlands
205
MICROW AVE SPECTRUM AND DIPOLE
MOMENT OF GL YCOLALDEHYDE
K.-M. MARSTOKK and HARALD M0LLENDAL
Department of Chemistry, University of Oslo, Blindern, Oslo 3 (Norway)
(Received June 16th, 1969)
ABSTRACT
The microwave spectrum of glycolaldehyde, CHzOH-CHO, has been measured and the rotational and centrifugal distortion constants ofthe ground and three
vibrational excited states have been obtained. Only one isomer, which has the
carbonyl and the hydroxyl groups cis to one another, was identified.
The dipole moment was determined to be 2.73 :t 0.04 D from Stark-effect
measurements.
INTRODUCTION
Glycolaldehyde has been found to exist as a monomer in the gas phase1 and
as a mixture of monomers and dimers in solution 1- 3. Its crystal structure is believed to be dimeric, having a dioxane structure4.5.
To obtain more detailed information about its structure, the IR and Raman
spectra have recently been examined6, and X-ray crystallographic work has been
initiated 7.
For monomeric glycolaldehyde various rotational isomers are theoretically
possible but only one form, with the carbonyl and the hydroxyl groups cis to ane
another, was identified. Deuterated speeies of the maleeule are now being studied
and we hope to establish its ro-structure.
EXPERIMENT
AL
Glycolaldehyde purum from Fluka AG was used without further purification.
The spectrum of glycolaldehyde was studied at room temperature in a conventional
Stark-effect speetrometer employing 50 kHz Stark modulation and phase-sensitive
detection.
J. Mol. Structure, 5 (1970) 205-213
206
L-M. MARSTOKK,a
M0LLENDAI
Frequency measurements were carried out with a frequency standard having
a stability of 0.05 p.p.m. and a calibrated communications receiver. The apparatus
was calibrated against lines of known frequencies. Additional calibration was perforrned against standard frequency broadcasts.
The spectral regions 12.3-18 GHz and 21.9-26 GHz were examined.
METHOD OF CALCULATION
Watson8 has recently shown that the energy, W, for a non-planar centrifuga
distorted rotor is given (correct to first order) by:
W = Wo - dJJ2(J+l)2-dJKJ(J+l)<P;)-dK<P;)-dwJWoJ(J+I)dWKWO<P;)
(1:
where Wo is the energy of the corresponding rigid rotor and db dJK, dK, dWb ane
dWK'are the five determinable centrifugal distortion constants.
To utilize formula (I) a computer program, MB07, was written. Wo, <P;)
<P;), <P;), and <P;) were calculated in the manne r described elsewhere9 using I
representation. The observed assigned frequencies were fitted using the stand are
least squares procedure*. The program yields the rotational and centrifugal distor.
tion constants, their standard deviations and correlation coefficients. The stand are
deviation of the frequencies, a, is also computed.
a
=
(2:
(~1(Vi-VObS)2/Nr
Here, Vi and Vobs.are the calculated
of observations.
Extended length arithmetics
and observed frequencies,
were used throughout
and N the numbe]
the computations.
THE MICROW AVE SPECTRUM
Preliminary rotational constants were calculated by combining the para.
meters of methanol1 o and acetaldehydell assuming the hydroxyl and the carbony
groups to be cis. A strong b-type spectrum was found whose features were dose te
the predicted one. The low J lines were identified on the basis of their very dem
Stark patterns, intensities, and only minor deviations from a rigid rotor fit. Thesf
absorptions were used in the program MB07 and an improved set of rotationa:
and centrifugal distortion constantswas obtained. From these constants the positions of medium J lines (J = 10-20) were caIculated and subsequently assigned,
* This part of the program was written by Dr. T. G. Strand.
J. Mol. Structure, 5 (1970) 205-213
MICROWAVE
SPECTRUM
207
OF GLYCOLALDEHYDE
By ineorporating these frequeneies in the least squares treatment, further improved
rotational and eentrifugal distortion constants were eomputed. By employing these,
the frequeneies of high J transitions (J = 20-33) were eomputed and found in the
vieinity of the ealculated ones. In this manner we were able to assign lines whieh
are distorted by as mueh as 780 MHz by eentrifugal forces.
Transitions belonging to the three first vibrational exeited states were identified in the same way as the ground state. They are listed as first, second, and third
exeited states aeeording to a rough estimate of their intensities. Neither the ground
state lines nor the three first exeited state lines were split.
The results of the least squares treatment is given in Table l, and the speetra
in Tables 2-5.
.BLE I
ILECULAR CONSTANTS FOR GLYCOLALDEHYDE
~rational
'te
Ground
state
First
excited
state
Second
excited
state
Third
excited
state
rmber of lines
49
40
35
33
MHz)
MHz)
MHz)
kHz)
,(kHz)
kHz)
18446.410
6526.042
4969.274
-27.14
-73.22
88.3
J
x 106
K
x
5.648
-3.40
0.089
3.1377
106
VlHz)
-t-IB-fc(amuA2)
::I:
::I:
::I:
::I:
::I:
::I:
::I:
::I:
0.026
0.008
0.012
0.54
0.72
1.4
0.096
0.12
18463.653::1:
0.024
6482.563::1:
0.007
4965.085::1:
0.01 1
-25.58
::1: 0.52
- 72.46 ::I: 0.53
95.0
::1:1.3
5.309 ::I: 0.097
-3.80
::1: 0.11
0.069
3.5457
18576.764::1:
0.042
6478.033::1:
0.012
4938.584::1:
0.021
-26.76
::1: 0.80
-78.66
::1: 0.92
92.2
::1: 1.8
5.52
::1: 0.17
-3.31
::1: 0.15
0.117
2.8872
18524.976::1:
0.038
6445.659::1:
0.010
4933.562::1:
0.019
-27.85
::1: 0.91
-80.72
::1: 0.90
95.2
::1: 1.7
5.82
::1: 0.18
-3.45
::1: 0.15
0.096
3.2510
nversion facto r 505531 MHz amuA2.
lcertainties are standard deviations.
T ABLE 2
MICROWAVE
SPECTRUM OF THE GROUND
Transition
JK-1,K+1
00,0
10"
20,2
2"2
-+
-+
-+
->
Observed
-+ PK' -l,K'
1",
1"0
2",
30,3
+1
STATE OF GLYCOLALDEHYDE
Calculated
frequency*
(MHz)
frequency
(MHz)
23415.72
13477.17
15176.62
23415.72
23415.678
13477.131
15176.639
23415.840
Centrifugal
dist. correction
(MHz)
-
0.018
0.009
0.003
0.638
(continued on p. 208)
J. Mol. Structure, 5 (1970) 205-213
208
K.-M. MARSTOKK, H. M0LLENDAI
TAB LE 2 (continued)
Transition
JK-bK+l
-+ J'K' -bK'
Centrifugal
dist. correction
(MHz)
-
0.174
-
2.046
0.546
1.006
0.856
-
6.999
5.229
-
15.575
25.621
-
5.074
4.915
31.079
38.291
11.332
11.265
-
51.132
54.917
-+ 33,1
-+ 33,0
-+ 41,3
15642.62
17716.34
22143.02
15642.741
17716.436
22142.888
-
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
12299.94
12804.11
15614.97
22252.79
22636.48
22685.92
15495.14
17786.66
24627.55
24639.98
14078.25
14759.52
12462.56
12495.80
12391.47
14451.90
14459.93
25175.49
24776.33
16430.50
16432.22
22750.59
22857.42
22374.92
22374.92
16516.85
16518.37
24366.61
24366.61
14446.98
12377.85
12377.85
14209.21
14209.21
24788.05
24788.05
16232.81
16232.81
22675.08
22675.08
12299.971
12804.101
15614.890
22252.756
22636.585
22685.957
15495.063
17786.613
24627.726
24640.029
14078.227
14759.496
12462.683
12495.669
12391.338
14451.816
14459.889
25175.344
24776.339
16430.401
16432.324
22750.562
22857.291
22374.907
22374.930
16516.784
16518.403
24366.628
24366.634
14446.948
12377.812
12377.724
14209.211
14209.215
24787.910
24788.119
16233.007
16233.002
22675.007
22675.058
42,2
53,3
63,3
84,4
84,5
105,5
105,6
105,5
105,6
126,6
126,7
126,6
126,7
136,7
136,8
147,8
157,8
157,9
157,9
157,8
178,9
178,10
178,9
178,10
2311'12
2311'13
231b12
2311'13
2512'13
2512'14
2512,13
2713,15
2713'14
2813,15
2813,16
2813'15
2813,16
3014,16
3014,17
3014016
3014'17
Calculated
frequency
(MHz)
17981.059
15261.614
-+
-+
40,4
Observed
frequency*
(MHz)
17980.93
15261.66
30,3
32,2
42>3
+1
3b2
41,3
62,4
72,6
93,7
93,6
96,4
96,3
114,8
114,7
117,5
117,4
135,9
135,8
127,6
127,5
156,9
148,7
148,6
166,10
166,11
169,8
169,7
187,12
187,11
2212,11
2212,10
2410'15
2410,14
2413,12
2413,11
2611>16
2812'16
2812,17
2714,14
2714,13
2912,18
2912'17
2915'15
2915'14
3113'19
3113018
* :1:0.05 MHz.
J. Mol. Structure,
5 (1970) 205-213
29.647
29.430
-
77.586
45.420
45.338
-108.911
-104.879
66.082
66.054
-143.594
-145.190
163.675
163.674
-305.611
-305.673
210.210
210.209
-377.726
-460.069
-460.063
353.427
353.426
-558.488
-558.502
430.064
430.058
-665.446
-665.447
MICROWAVE
SPECTRUM
209
OF GLYCOLALDEHYDE
TABLE 3
MICROWAVESPECTRUMOF THE FIRST EXClTED STATE OF GLYCOLALDEHYDE
Transition
JK-1,K+l -+ J'K' -1,K' +1
00,0
10"
20,2
21,2
30,3
32,2
40,4
63,3
-+
-+
-+
-+
-+
-+
-+
-+
1",
11,0
21,1
30,3
3'>2
41>3
41,3
72,6
84,4
94,5
105,5
105,6
105,5
105,6
126,6
126,7
126,6
126,7
136,7
136,8
136,7
157,8
157,9
157,8
157,9
21'0'11
21,0,,2
2311"2
23'1,13
23'1,12
23,1,,3
24,1,,3
2411"4
2612"4
2632,,5
2612"4
2811,,5
2813"6
32'5"7
32'5"8
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
93,7
103,8
96,4
96,3
114,8
114,7
117,5
117,4
135,9
135,8
127,6
127,5
145,,0
148,7
148,6
166,11
166"0
229,,4
229,13
2212,11
2212,'0
24'0"5
24'0"4
2312>12
2312,11
2513>13
2513"2
2711'17
27'4"4
27,4,13
33,4,20
33,4,,9
Observed
frequeney*
(MHz)
Caleulated
frequency
(MHz)
Centrifugal
dist. correetion
(MHz)
23428.68
13498.58
15151.35
23209.60
17872.68
14773.65
21904.59
12492.76
23428.736
13498.573
15151.297
23209.686
17872.617
14773.589
21904.660
12492.700
-
14913.44
25723.07
23678.38
23721.47
14469.44
16531.00
25867.99
25878.55
12793.56
13388.35
13789.07
13817.12
25189.35
15977.35
15983.91
23170.31
23508.92
16375.53
16380.66
24704.83
24704.83
14103.12
14104.38
12603.89
12603.89
14813.70
14813.70
24185.97
17030.45
17030.45
17249.54
17249.54
14913.319
25723.234
23678.499
23721.459
14469.361
16531.051
25868.028
25878.430
12793.477
13388.290
13789.096
13817.005
25189.384
15977.285
15983.921
23170.201
23509.008
16375.448
16380.685
24704.862
24704.880
14103.174
14104.397
12603.789
12603.834
14813.675
14813.685
24185.981
17030.486
17030.488
17249.532
17249.551
0.007
0.002
0.043
- 0.615
- 0.074
- 1.983
0.642
-- 5.500
- 15.796
- 22.338
-
4.598
4.461
31.139
-
37.603
10.624
10.567
-
50.964
54.261
29.097
28.914
-
71.883
44.626
44.559
-104.371
-107.795
-241.612
-241.764
161.031
161.031
-303.807
-303.854
226.191
226.188
283.509
283.509
-460.593
349.721
349.721
-780.632
-780.622
* :1::0.05 MHz.
J. Mol. Strueture, 5 (1970) 205-213
210
K.-M. MARSTOKK,
H. M0LLENDAL
TABLE 4
MICROWAVE
SPECTRUM OF THE SECOND EXCITED STATE OF GLYCOLALDEHYDE
Transition
JK-1,K+1
-+J'K'-1>K'+l
00,0
10,1
20,2
21>2
-+
-+
32,2
-+ 41>3
-+
-+
40,4
-+
-+
84,4
-+
84,5
84,4
-+
94,5
-+
105,6
-+
105,5
-+
105,6
-+
-+
115,6
115,6
-+
136,7
-+
136,s
-+
136,s
-+
199>11 -+
199,10 -+
2110'11 -+
2110'12 -+
2210,13 -+
2210'12 -+
2210'13 -+
2411>13 -+
2411'14 -+
2411,13 -+
2411>14 -+
2813,15 -+
2813,16 -+
3014>16 -+
3014,17 -+
3014,16 -+
3014'17 -+
11,1
11>0
21>1
30,3
41>3
75,3
75,2
93,7
103,s
96,3
114,s
114,7
106,5
124,9
127,6
127,5
145,9
1810,S
20S,13
229>14
229,13
2111>10
239,15
239>14
2312'12
2312'11
2510'16
2510>15
2912,lS
2912'17
2915'15
2915'14
3113,19
3113>18
Observed
Calcu/ated
frequency*
(MHz)
frequency
(MHz)
23515.25
13638.19
15315.44
23008.19
23515.312
13638.160
15315.390
23008.337
14366.04
14366.059
22172.00
22806.42
22980.61
13744.02
24503.23
25407.82
13026.16
15142.71
13266.02
24990.50
15803.13
15831.98
24691.90
23275.94
15978.14
13390.35
13396.00
13663.91
25839.49
25851.92
16174.31
16174.31
23200.08
23203.07
17954.89
17954.89
23737.80
23737.80
15338.92
15338.92
22172.076
22806.537
22980.602
13743.906
24503.327
25407.836
13025.782
15142.512
13265.910
24990.387
15803.030
15831.947
24691.835
23276.052
15978.173
13390.292
13395.783
13663.930
25839.495
25851.798
16174.195
16174.244
23200.021
23202.969
17954.725
17954.881
23737.931
23737.929
15338.826
15338.846
Centrifugal
dist. correction
(MH")
-
0.010
-
0.002
0.034
-
0.603
1.956
-
0.713
-
0.069
-
0.367
- 15.003
- 21.359
2.181
- 29.763
- 36.597
15.498
- 42.962
25.312
25.117
- 77.793
78.876
-179.805
-229.847
-230.010
161.091
- 292.009
-292.411
205.128
205.126
-361.141
-361.268
-528.580
-528.580
383.252
383.250
-627.798
-627.816
* ::1::0.10 MHz.
OTHER ROTAMERS
Presumably other rotamers of glycolaldehyde would have sizeable dipole
moments. A search was made, but no absorptions having characteristic Stark
patterns were found. In addition, more than 90 % of the strong lines of the specJ. Mol. Structure, 5 (1970) 205-213
MICROW AVE .sPECTRUM
OF GLYCOLALDEHYDE
211
TABLE 5
MICROWAVESPECTRUMOF THE THIRD EXCITED STATEOF GLYCOLALDEHYDE
Transition
Observed
Calculated
JK-1.K+1-+ J'K' -l.K' +1
frequency*
(MHz)
frequency
(MHz)
23458.50
13591.41
15236.81
22910.15
17943.80
14192.13
21952.02
23458.551
13591.411
15236.778
22910.261
17943.744
14192.054
21951.88
-
25742.20
22866.12
23029.65
24408.62
25441.98
25482.97
12826.59
14818.04
15964.59
15990.86
23117.80
23510.16
15563.18
15583.58
12951.09
12955.84
16525.68
16525.68
22659.32
22661.83
17361.80
17361.80
24174.13
24174.13
14717.63
14717.63
25742.267
22866.111
23029.502
24408.744
25442.097
25483.070
12826.376
14817.929
15964.545
15990.874
23117.668
23510.258
15563.269
15583.421
12950.951
12955.729
16525.576
16525.617
22659.288
22661.815
17361.694
17361.823
24174.241
24174.240
14717.667
14717.541
-
00,0
-+
1",
10"
20,2
2"2
30,3
32,2
40,4
-+
-+
-+
-+
-+
-+
1"0
2",
30,3
3"2
4"3
4"3
63,4
84,4
84,s
94,s
105,5
105,6
105,5
105,6
136,7
136,8
136,7
199,,,
199,,0
199,,,
21'0'"
21'0"2
24",13
24""4
24""3
24""4
2813,,5
2813"6
30,4,,6
30,4,,7
30,4,,6
30,4,,7
-+
-+
-+
72,s
75,3
75,2
103,8
96,4
96,3
114,8
114,7
127,6
127,5
145,,0
18,0,8
208,,3
208,,2
229,,4
229,,3
2312'12
2312'"
25,0,,6
25'0"5
2912,,8
2912"7
29'5"5
29'5"4
31,3,,9
31,3,,8
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
-+
Centrifugal
dist.correction
(MHz)
-
-
0.014
0.006
0.025
0.657
0.124
2.081
0.767
14.117
0.375
0.084
-
23.032
3.253
3.113
- 31.750
- 38.434
27.794
27.610
- 73.734
86.643
-190.917
-191.371
-244.396
-244.543
221.834
221.832
-383.048
-383.161
- 561.885
-561.897
415.476
415.477
-668.271
-668.103
* :1::0.10 MHz.
trum were assigned to the cis form by the least squares procedure described above.
For these reasons we do not believe that other rotamers exist in any appreciable
concentration at room temperature.
DIPOLE MOMENT
The displacement of the Stark lobes as a function of the applied electric field
was used to determine the dipole moment. The l ---+ 2 transition of COS was used
J. Mol. Structure, 5 (1970) 205-213
212
L-M.MARSTOKK,H.M0LLENDAL
to calibrate
small
the electric field inside the cell (employing
instability of the square
ponents
of the 21,2 ~
since they
have
generator,
30,3 transition
comparatively
this instability. The
wave
slow
were
Stark
only
used
/1e05
M
=
= 0.71521012).Due toa
O and
to determine
effects which
results of a series of measurements
were
M
=
1Stark
the dipole
almost
are given
com-
moment
unaffected
in Table
by
6. We
= 0.12::1::0.04D,
/1B= 2.73::1::0.03D and /1 = 2.73::1::0.04D.
In the calculations it was assumed that the C-component of the dipole
moment vanishes. The theoretical expressions for the Stark coefficients were calculated by the program MB049.
find'/1A
TABLE 6
STARK COEFFICIENTS
AND DIPOLE MOMENT OF GLYCOLALDEHYDE
Llv/E2
[MHz/(kVem)2]
Obs.
Cale.
M=O
+3.26:1::0.04
3.286
M=!
+ 1.82:1::0.03
1.806
21,2 --* 30,3
flA = 0.12:1::0.04 D
flB = 2.73 :1::0.03 D
fl = 2.73:1::0.04 D
DISCUSSION
Structure
The value lA+IB-lc = 3.1377amuA2 is typical of a moleculehaving two
out-of-plane hydrogens (see, e.g., ref. 13). Two forms of glycolaldehyde would
be compatible with this. Model calculations using bond angles and distances from
acetaldehydell and methanollO, assuming the carbonyl and hydroxyl groups to be
ds, yielded rotational constants which were in good agreement with the observed
ones. A model having the two groups trans gave rotational constants which were
in obvious disagreement with observations.
Vibrational information
The variation of lA +IB-lc in various vibrational states has been found useful in making assignments14,15. The increase of lA +IB-Ic from 3.1377 amuÅ 2 for
the ground state to 3.5457 amuA for the first excited state is typical for an out-ofJ. Mol. Strueture, 5 (1970) 205-213
MICROW
A VE SPECTRUM
OF GL YCOLALDEHYDE
213
plane vibrationl4. Presurnably this is therefore the first excited state of the C-C
torsional mode.
lA +IB-Ic of the second excited state is smaller than that of the ground state.
This is expected for a low frequency in-plane model4.
The assignment of the third excited state is more uncertain. It could be the
lowest combination state of the C-C torsional and skeietal modes, or it could be
another low skeietal deformation mode.
Centrifugal distortion
As expected, the centrifugal distortion constants of the various vibrational
states of glycolaldehyde differ only slightly. However, some of them are found to
be significantly different from one vibrational state to the other as can be seen from
Table 1. This indicates that the study of centrifugal effects of various vibrational
states of a molecule should provide additional information with regard to the
force field.
ACKNOWLEDGEMENTS
We wish to thank Dr. T. G. Strand for giving us his generalleast squares
program. Civ. ing. Birgit Andersen is thanked for giving us her interatomic distance
program. Financial support from the Norwegian Council for Science and Humanities is gratefully acknowledged.
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