Microwave spectra, molecular structures, and theoretical calculations of ( E)- sp and ( E)- ac isomers of 2-methylpropanal oxime

Abstract

The microwave spectra of two conformers of ( E)-2-methylpropanal oxime ((CH 3) 2CH CH NOH) and its deuterated species ((CH 3) 2CH CH NOD) were observed in the frequency range from 8 to 40 GHz. The absorption lines in the ground and excited vibrational states were assigned. The rotational constants of normal species in the ground vibrational state were determined to be A = 7343.5(25), B = 1847.20(2), and C = 1607.29(2) MHz for ( E)- sp isomer and A = 7073.15(84), B = 2006.01(1), and C = 1686.62(1) MHz for ( E)- ac isomer. The planar moments ( P bb = ( I c + I a − I b )/2) of the normal and deuterated species were determined to be 54.829(15) and 54.829(8) uÅ 2 for the ( E)- sp, and 59.578(6) and 59.768(7) uÅ 2 for the ( E)- ac, respectively. The P bb values of the ( E)- sp of normal and deuterated species suggest that the ( E)- sp has C s symmetry. The r s coordinates of the hydrogen atoms of the hydroxyl group were determined for the ( E)- sp and the ( E)- ac. They indicated that their OH bonds took trans positions with respect to the C N double bond. The four and six structural parameters were adjusted by fitting to the rotational constants of the ( E)- sp and ( E)- ac, respectively. The observed rotational constants ( B and C) of the ( E)- sp and the ( E)- ac isomers were in better agreement with those calculated using the MP2/6-31++G( d, p) level than with those calculated using the MP2/6-31G( d, p) level.