The molecular structure of dimethyl ethyl amine in the gas phase, determined by electron diffraction

Journal

of Molecular

Elsevier Scientific

Structure,

65 (1980)

303-304

PublishingCompany,Amsterdam- Printedin The Netherlands

Short communication

THE MOLECULAR STRUCTURE THE GAS PHASE, DETERMINED

JOS H. M. TER BRAKE, Goriaeus

(Received

Laboratories,

12 November

VINCENT

P.O.

Box

OF DIMETHYL ETHYL AMINE BY ELECTRON DIFFRACTION

MOM and FRANS

9502,

2300 RA

Leiden

IN

C. MIJLHOFF (The

Netherlands)

1979)

The structure of dimethyl ethyl amine has not been determined previously. In anticipation of a more sophisticated analysis which, due to lack of spectroscopic data, will be rather time consuming, we wish to report the ra structure determined by gas-phase electron diffraction. The data were recorded, using a commercial sample, by Balzers’ equipment at Leiden at 20, 34 and 59 cm camera distance, using 40 kV electrons. The nozzle was at room temperature. As usual the levelled intensities T(s)/B(s) were used for a least squares fit of 1 + RM(s) calculated from the molecular model, weights taken proportional to s/s,,,. Only one conformation is present; the N-methyl groups gauche and Pans (Fig. 1). Obviously the steric hindrance prevents thegauche-gcruche conformation from being present in detectable amounts. In evaluating the geometry the following assumptions were made: (a) all methyl groups have local C3” symmetry and the same geometry; (b) the methylene and methyl C-H distances are equal. The electron diffraction data do not allow resolution of differences, if any, between the C-N bond lengths or C-N-C bond angles, which have estimated standard deviations of 0.15 a and 5”, respectively. Therefore, the differences were fixed at zero. The following geometry was obtained (error limits 30 in parentheses): r(C-N) = l-452(6) a, r(C-C) = l-539(24) A, r(C-H) = l-106(4) a, LC-N-C = 111.3(1.0)“, LN-C-C = 113(3)“, LC-C-H = LN-C-H = 113(3)“, TC-C-N-C = 74( 4)O. The other skeletal torsional angles, given in Fig_ 1, have errors (30) of about 6”. The N-methyl groups are virtually staggered. The torsional angle of the C(2) methyl group (76.3 + 10” ) suggests a departure from the staggered position in response to the steric interaction with the C(4) methyl group. That this interaction must be considerable is clear from the large value of r C-C-N-C. That the molecule is performing rather strong torsional vibrations is evident from the r.m.s. amplitudes of C(2) . . . C(3) and C(2) . . . C(4), which are 0.079 (18) and 0.15 (1) a respectively. 0022-2860/80/0000-0000/$02.25

0 1980

Elsevier Scientific Publishing Company

304

Fig. 1. Newman

projection

of dimethyl

ethyl

amine.

The structure compares well with that of N(CH,)3 [l] . The C-N-C bond angles 110.9” + 1.8” (30) are equal. The 5 C-N bond length is 1.461 + 0.006A. If we add u*/r to our value (U = 0.052 (6) A) we arrive at 1.454 rt 0.006 A as an estimate of 5. The difference, although within the limits of error, may be less if shrinkage effect is taken into account. REFERENCE 1

B. Beagley and A. R. Medwid, J. Mol. Struct., 38 (1977) 229.