The infrared spectrum of 3-methyldiazirine

JOURNAL

OF MOLECULAR

The

SPECTROSCOPY

Infrared

29,

174-182 (1%)

Spectrum

R. W. U. S. Army Missile

MITCHELL

Command,

of 3-Methyldiazirine AND

J. A.

MERRITT

Redstone 9rsena1,

Alabama

95809

Vapor and solid phase infrared spectra have been obtained for 3-methyldiazirine in the 25&4000 cm-l region. Vapor phase band contours, characteristic group frequencies, and the vibrational assignments for other substituted diazirines were used in assigning the fundamental frequencies. All fundamentals were observed except the CHI torsion which normally occurs below 250 cm-l.

INTRODUCTION Diazirine and a number of its substituted derivatives have been of considerable interest to both chemists and spectroscopists since they lvere first prepared (1, 2). This laboratory has been engaged in spectroscopic studies of several of these substituted diazirines (s-5). The study of the infrared spectrum of 3methyldiazirine,

is a continuation of this series. The vapor and solid phase infrared spectra of this molecule in the 250-4000 cm-l region have been obtained; and from vapor phase band contours characteristic group frequencies, and vibrational assignments for other substituted diazirines, the vibrational fundamentals have been assigned. EXPERIMENTAL METHODS The 3-methyldiazirine mas prepared by the method of Graham (6). It was purified by gas liquid chromatography at ambient temperature (~23°C) using a Beckman Megachrom preparative gas chromatograph, equipped with four :‘y in. X 12 ft. parallel columns packed with Apiezon J on firebrick. A methylcyclohexane-liquid nitrogen bath (- 126°C) \vas used to trap the sample. The CO2 and Hz0 were removed u-ith Ascarite and magnesium perchlorate on a vacuum line. Purity of the sample was confirmed by mass spectral analysis. All infrared spectra were taken Tvith a Beckman IR7 spectrophotometer equipped with a cesium iodide interchange unit to extend the range to 250 cm-‘. Vapor phase spectra were recorded with varying pressures in a lo-cm cell. The solid phase spectrum was obtained with the sample deposited on a cesium iodide 174

IR SPECTR,UM

OF 3.METHYLDIAZIRINE

FIG. 1. Schematic of the X-methyldiazirine of the principal axes.

molecule

with the approximate

175

orientation

substrate kept at 77°K with an Andonian Dewar .l Vapor phase frequencies were determined by interpolating het’ween hewn rotational frequencies of a calibrant gas (7). DISCUSSION ,$H

in met.hylchloroand methylbromodiazirine, 3-methyldiazirine is treated as belonging to t’he symmetry group C, , wit,h the symmetry plane lying along the HCC bonds and normal to the plane of the ring. There are 18 fundamental vibrations: 1 la’ + 7~“. A schematic of the molecule in Fig. 1 shows the approximate orientation of the principal axes. The parameters given for the ring are those established for diazirine by microwave spectroscopy (8), and the remainder have been estimated from known values for other molecules. The symmetry plane contains the A and C axes, and therefore all a’ vibrat,ions should be revealed by either -4, C, or -4-C hybrid type band contours (9). Vibrations antisymmetric to the symmetry plane should give rise to type B bands. The moments of inertia about the principal axes have been calculated from the parameters shown in Fig. 1 to be I, = lS.6OJ, fh = 74.151, and I, = 79S93 amu-k. The x-axis was chosen as passing through the ring carbon atom perpendicular to t,he NK bond. Figure 2 shows a recorder trace of the vapor phase spectrum of 3-methyldiazirine. The absorption band at 200 cm-’ is due t’o the cesium iodide windows of t,he cell, fore prism, and thermocouple of the monochromator. The very weal; band at approximately 547 cm-’ is apparently due t,o an impurit.y since it. was 1Andonian Associates,

Inc., 26 Thayer

Road,

Waltham,

Mass. 02151.

176

MITCHELL

4000

3600

3200

0 1400

1200

2800

2400

AND

MERRITT

2000

\*I .

1000

1600

1800

1400

1.

800

600

400

200

cm-’ FIG. 2. Vapor phase infrared spectrum of 3-methyldiazirine. Spectrum (A) was obtained with 260 mm pressure and (B) and (C) with 115 mm and 71 mm, respectively.

not observed in the spectrum of a different sample. Considerable splitting can be seen in the bands near 1100 and 1400 cm-[ in the solid phase spectrum shown in Fig. 3. In the other bands, however, splitting is either absent or very slight. The broad band at approximately 3300 cm-’ is due to water, and the bands near 900 and 1200 cm-1 are apparently due to some impurity or to the cesium iodide substrate. The vapor and solid phase frequencies, relative intensities, vapor phase band types, and the assignments for 3-methyldiazirine are given in Table I. Table II contains approximate descriptions of the vibrations and the vibrational assign-

177

IR SPECTRUM OF 3-METHYLDIAZIRINE 100

z

0

6O

/L‘, p++l

‘1 ,, I/ )

i

@++\

bf

* vI60’ z ul 240.

a

I c X20.

iq,

+py

\: N ’ I\ 8,1

)~ ‘i

\I

/I

il

I’

I

I I

0 4000

JbOO

3200

2600

2400

2000

1600

1600

1400

cm-’

1400

1200

1000

600

600

400

200

cm-l FIG. 3. Solid phase infrared spectrum of 3-methyldiazirine obtained without a matrix at 77°K.

ments for 3-methyldiazirine and the previously assigned frequencies of these vibrations in methylchlorodiazirine, methylbromodiazirine, and 3,3-dimethyldiazirine. The assigned frequencies for these molecules are utilized in making the assignments for 3-methyldiazirine and are included here rather than making specific mention of each in the text. a’ Vibrations In 3-methyldiazirine there are three CH, stretching vibrations and three CH, deformations. From the spectra of the other substituted diazirines, the two stretching frequencies in this species are expected to occur slightly below 3000

178

MITCHELL

AND

MERRITT

cm-l and should have A, C, or A-C hybrid type bands. Three bands occur below 3000 cm-’ as potential candidates for these vibrations: 2987.7, 2937.4, and 2876.1 cm-l. The 2987.7 and 2937.4 cm-l bands occur near the frequencies assigned as fundamentals in other diazirines with methyl groups and appear to be due to the t,wo a’ CHs stretching modes. The 2987.7 cm-’ is assigned t’o the nonsymTABLE

I

Observed Vapor and Solid Phase Vibrational Relative Intensities, Band Types, and Assignments Solid

Vapor

cm

Relative* intensity

-1

Band type

’ cm

-1

AorC

1387.8,

m

B

1446.0

S-VS

m

A

1450.6

m

?

1556.9

m

“S

A

1599.9

s-“S

m-S

A?

1773

w

broad

1935.3

w

A

1964.4

w

A

2038.2

VW

A?

2221

w

A?

0 Q

1404

R

1447.0 1463.

3

VW?

1542.8

1585.

5 Q

1597

R

1617.7

Q

1626

R

1395.8

Relative* intensity

S

1392.

Frequencies, for 3-Methyldiazirine

m

Assignment

‘6

v13 v5

“4

2v16

‘6

+ ‘17

2v15 v

8

= 1602.8

tv

= 1938.6 10

v14 + v15 ‘6

= 1774.5

+ ‘10

= 1967.6 = 2040.

9

= 2222.7

*The letters used here have their usual meaning: VW 2 very weak, w = weak, m = s = strong, vs = very strong, and combinations of these for borderline cases. medium,

IL1 SPE(?TRUM

TABLE

I (Concluded)

Observed Vapor and Solid Phase Vibrational and Assignments Relative Intensities, Band Types,

-1

Frequencies, for 3-Methyldiazirine

Solid

Vapor

cm

1i!)

OF 3.METHYI,DIAZIttINE

Relative*

Band

intensity

type

cm

I

-1

Assignment

Relative* intensity

I v 8 = 2495.

2490

w

A

2740

w

A

2765

w

A or C

2876.1

w

A

2900

VW

2937.4

S

A

2930

w-m

2967.2

S

B

2970.4

n-l

2987.7

S

AorC

2980.8

w

S

A

3053” 9

m

3188

VW

broad

ternary

3894

VW

broad

ternary

3052.

5, 3060. 2

:::The letters medium,

used here

s = strong,

have their

vs = very

usual

strong,

v7

t

‘8

+ “16

5

= 2739.7

2~15

t

vlo

2v13

= 2894

= 2769.

3

v3 v12 v2 “1

meaning: VW = very weak, w = weak, m = and combinations of these for borderline cases,

metric a’ C-H stretching in the methyl group and bhe 2937.4 cn-’ to the symmetric a’ C-H stretching. The 3876.1 cm-’ band is possibly an overtone of v13 that is pushed to a lower frecnrency by interactSion mit)h t,he 3937.1 cn~-~ fundamental. A band representative of t,he stretching of the lone proton on the ring carbon :ttom should also be observed in this region. The band cont80ur should be type A, C’, or A- (J hybrid, and since the prot’on is attached t’o the carbon atmom bonded to the two nitrogen atoms and the methyl group, it is expected t,o occur slightly above 3000 cnr+. h st’rong band wit,h a two component’ Q-branch occurs at 30.52.5, 3060.2 err-’ which appears to be due to this vihrat~ion, and it is t,hus assigned. Characteristic group frequencies and t’he assignments for ot#her diazirines reveal that, one of the a’ CH3 deformation frequencies should occur near 1390 cn-’ and t,he ot,her near 14.50 rxnL. 4 band wit’h eit’her type A or type (i cont’our is observed at, 1392.0 cn+ in the vapor phase speckum and is assigned to the symmetric deformation mode. The nonsymmetric mode is assigned to the hand :~t 1463.3 cm-’ which appears to have :I type ‘4 band envelope.

lS0

MITCHELL

AND TABLE

MERRITT II

FUNDAMENTAL FHEQUENCY ASSIGNMENTS (cm-l)

FOH 3-METHYLDIAZIRINE AND T~osrc

FROMTHE LITERATURE FOR SIMILAR VIBRATIONS IN METHYLCHLOROw), Species

a’

AND 3.3..DIMETHYLDIAZIRINE

Approximate Description

CH3ClCN2

(CH&CNz

CHs(H)CNz

-

3052.5, 3060.2 2987.7 2937.4 1585.5 1463.3

nCH3 stretch” sCH3 stretch NN stretch nCH3 deformation

3001.8 2945.9 1573.4 1463.1

2994.8 2941.8 1571.3 1453.4

2995a, 2933a1 1586a1 1458,

, b2 , b2

sCH3 deformation

1385.4

1431al 1389,

, b::

1390.1

13Qlal -

, h2

CH (in-plane) CHa rock

bend

CC (in-plane) &HZ stretch

1071.6 891.5 -

bend

2990.5

nCH3 deformation CHS rock CH (out-of-plane) CN stretch

bend

CC (out-of-plane) CH, torsion

bend

’ 12 = nonsymmetric;

1107.8

CN stretch CC stretch a”

CH3BrCN2

-

CH stretch

(S), METHYLBROMO-

(4)

1443.2 1020.3 868 -

1090.8 1090.9 873.8 2988.5 1437 .o 1010.6 858 -

1392.0

987.6, 958a1 , bl 1136al 738al 2960.2bl 1469.6bl 1110bl 788.1bl -

1358.5 1136.9 1094.9 830.7 435.5 2967.2 1447.0 1071.6 969.3 801.4 382.5 -

s = symmetric.

Another band with medium intensity occurs at 1358.5 cm-l. This band is a potential candidate for the in-plane bending vibration of the proton attached to the ring carbon atom. The frequency is slightly higher than might be expected, but the band cannot be explained very well by an overtone or combination and is assigned to this vibration. In the vibrational assignments for the substituted diazirines with a single methyl group the a’ CH, rocking vibration was observed near 1100 cm-l. In methylcyclopropane fitrerdlov and Brainov assigned this vibration at 1017 cm-’ (IO), and in acetyl chloride it has been assigned at 1109 cm-’ (11). We observe a band at 1136.9 cm-l in the vapor phase spectrum of 3-methyldiazirine which has either type A or type C band contour. This band occurs in the expected region, has the proper band contour, and is therefore assigned to the a’ CH, rocking vibration. The N=N stretching vibration was assigned in t,he infrared spectrum of diazirine at 1626 cm-l (1Z), but from the electronic spectrum, it appeared to be at 1606 cm-l (18). In difluorodiazirine the band appeared at 1.563 cm-’ (14). The

IR SPECTRUM

OF 3-METHYLDIAZIRINE

181

3-methyldiazirine spectrum reveals two bands near 1600 cm-l. One is at 1585.5 cm-’ and appears to be t’he strongest band in the spectrum. The other occurs at 1617.7 cm-l and is also strong, but is somewhat weaker than the 1585.5 cm-’ band. Both bands appear to have type A contour with the R branch of the 1585.5 CII-~ band overlapping t’he P branch of the 1617.7 cm-’ band. The solid phase spectrum reveals a single band at 1599.9 cm-‘. The 1585.5 cm-l band is assigned to the n’=N stretching fundamental, and the 1617.7 cm-l band appears to be due t,o an overt,one or combination that is in Fermi resonance with the fundament#al and is borrowing int’ensity from it. The first, overtone of the 801.4 cm-l band, which is assigned to the antisymmetric (r---X st,ret’ching vibration, should occur near 1603 cm-‘, and if the 1617.7 cnl-’ band is due t,o this overt#one, there is an upward frequency shift of at least 15 cnl-I. Under the above conditions, the fundamental should also be shifted, but] to lower frequencies. A 15 cm-l shift would put the undisturbed fundamental at 1600 cm-‘. This is supported by the single band in the solid phase spectrum at’ 1599.9 cn~-‘. Also, in the vapor spectrum of a partially deuterated sample, a single strong band is observed at 1599 cm-‘. A very weak band is observed in the :S-methyldiazirine spectrum at 1542.8 cm-‘. This band cannot be assigned as an overtone or binary combination of any observed fundamentals. The symmetric C--N stret.ching vibration has been assigned in the three methyl substituted diazirines between 1071.6 and 1136 cxx-I. The band at 1094.9 cnl-’ in the 3-methyldiazirine spect’rum occurs within these limits, appears t#o be :t type A band, and is assigned to this vibration. Jones and Sandorfy have suggested that C---C stretching frequencies in straight chain molecules have been observed over t,he 800-1150 cm-l region and the C-C bending frequencies below 500 cm-’ (In). A weak to medium intensit,J band occurs in the 3-methyldiazirine spectrum at 830.7 cm-l which appears to have t’ype 9 band contour but is somewhat overlapped by t,he band at 801.4 cm-‘. The C-C stret’ching vibration is assigned to this frequency. Two bands occur below 500 cm-l in the spectrum: 3S2.5 and 435.5 cm-‘. The 435.5 cm--’ band has type A band contour and is assigned to the C-C in-plane bending mode. a” I’ibrations

.Iccording to Fig. 1, vibrations antisymmetric to the symmetry plane should be revealed by bands wi-ith type B contour. There appears to be a type B band at’ 2967.2 cm-’ that is partially obscured by t’he R branch of the 2937.4 cm-l and the P branch of the 2987.7 cm-’ bands. Since this is the only t,ype B band in this region and ot’her bands have been assigned already, we assign it to the C--H stret’ching vibration in this species. The CH, deformation vibrat,ion in t,his species should be observed near 1400 cm-‘. A band with type B contour is observed at 1447.0 cnl-’ and is therefore assigned t,o this vibrat,ion. The CH3 rocking vibration is expect,ed to occur near 1100 cm-l, and we assign

lS2

MITCHELL

AND MERRITT

it t,o the type B band at 1071.6 cm- l. The only fundamental band in the spectrum which appears t,o be unperturbed occurs at 969.3 cm-l. It, is somewhat removed from the other fundamentals, has type B contour, and is assigned to the C-H out-of-plane bending vibration. Two bands remain unassigned in the fundamental region of the spect#rum: 801.4 and X32.5 cm- I. There are three vibrations yet to be assigned: the antisymmetric C--i\’ stretch, C-C out-of-plane bend, and CHs torsion. The C-C bending mode, as stated earlier, should occur below 500 cm-’ and is assigned to t#he type B band at, 3823 cm-‘. The antisymmetric C-S stretching vibration is t,hen assigned t#o the band at, 501.4 cm-l. ;\lethyl torsional modes about a C-C bond have been observed at frecluencies below t,he spectral region present,ly under consideration (16’). ACI~NO~~LI~I)G~~I’.U’L’S II The authors wish to express their indebtedness to Drs. Joseph Bierou aud W. H. Graham and Mr. Kirt Keller for supplying us with 3-methyldiazirine samples. Also, we would like to express our thanks to Drs. Frederick Hartman and William Knopka who diligently sought to make high purity deuterated derivat,ives of 3-methyldiazirine. RECEIVED:

June 29, 196s REFERENCES

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Lette?‘s 1261, 612; Chern.

Rer.

96, 795 (1962); 94,

2166 (196lj. W. H. GR.IH,~IM,J. .,L))L.(‘hen&. Sot. 84, 1063 (1962). R. W. MITCHELL )~NDJ. A. MERRITT, J. Mol. Spectry. 22,165 (1967). R. W. MITCHELL ANU J. A. MERRITT, J. IMoZ. Spectry. 27, 197 (1968). L. C. ROBERTSON ANL)J. A. MERRITT, J. Mol. Speclry. 24, 44 (1967). W. H. GRAH.~M, J. Am. Chem. Sot. 88, 4677 (1965). INTERNATI~N.Q, UNIOX OF Pcr~xrs;ASD APPLIRD CHEMISTRY, Pwe Appl.

699 (1961). 8. L. PIERCE AXD V. l>olru~us, J. ulna. C~PVL.Sot. 84, 2F51 (1962). 9. R. M. B.~DG~R AND L. R. ZU~~V~\LT,J. Chem. Phys. 6,711 (1938). 10. L. M. SVERDLOV AND E. P. KRAINOV, Opf. i Spektroskopiya 7,296 (1959). 11. J. OVEREND, 13. A. NYQTJIST, d. C. EVIINS, I\NDW. J. POTTS, Spectrochim.

Chem.

Acta

1, 537m

17, 1205

(1961). 12. 11.ETTINGICR,J. Chm. Ph,ys. 40, 1093 (1964). IS. L. C. ROBERTSON .\NIIJ. A. MERRITT, J. Mol. Spectry. 19,372 (196(i). 14. C. W. BJOIX, N. C. Crz.zrc, R. A. MITSVH, .\so J. OVRRII:ND,J. 9m. Chenc. See. 87, 1186 (1965). 15. It. N. JONES .ZNDC. S~NDOI~BY,“Chemical Applications of Spectroscopy,” pp. 350, 351. Wiley (Interscience), New York, 1956. 16. W. G. F.ZTXLF:Y .\NDF. il. MILITIA, Spectrochim. ilcta 17,857 (1961); 18,977 (1962).