Microwave spectrum, molecular structure, dipole moment, and quantum chemical calculations of s-trans-(E)-2-methyl-2-propenal oxime

The spectroscopic constants of s-trans-(E)-2-methyl-2-propenal oxime (methacryl-aldehyde oxime) of normal, H2C=C(CH3)-CH=NOH, and its deuterated species, H2C=C(CH3)-CH=NOD, were determined by observing their microwave spectra in the frequency range of 8 to 40 GHz in the ground vibrational state. The rotational constants were A = 8321.38(82), B = 2076.09(1), and C = 1678.60(1) MHz for normal species and A = 8283.7(16), B = 1998.63(2), and C = 1626.21(2) MHz for deuterated species, respectively. The inertial defects (Delta I = I-c - I-a - I-b) of normal and deuterated species were determined to be -3.09(2) and -3.10(3) u angstrom(2), respectively. The dipole moments were determined as mu(a) = 0.53(2), mu(b) = 0.27(2), and mu(total) = 0.60(5) D. The N-14 nuclear quadrupole coupling constants were determined as chi(aa) = 3.62(12), chi(bb) = 5.1(14), and chi(cc) = 1.48(26) MHz. The comparison of the observed spectroscopic parameters with the calculated ones led to the conclusion that the assigned spectrum was due to s-trans-(E) form. The r(s) coordinates of the hydrogen atom in a hydroxyl group were determined and the OH bond was found to be at the trans position with respect to the C=N double bond. The structural parameters of r(C-2-C-3), r(C-2-C-6), < C2C3N and < C6C2C3, for s-trans-syn form were adjusted to the four observed rotational constants (B and C). The observed rotational constants for s-trans-(E) form were in good agreement with those calculated using the MP2/6-31 G (d,p) level of theory. (C) 2017 Elsevier Inc. All rights reserved.