Structure and dynamics of methacrylamide, a computational and free-jet rotational spectroscopic study

The conformational space of methacrylamide was explored by quantum mechanical modeling and surveyed in the 59.6–104.0 GHz frequency range using a millimeter-wave Stark-modulated free-jet absorption spectrometer. According to relative orientation two unsaturated bonds, conformers were observed, namely s-trans (A=5234.360(1), B=3364.9717(8) C=2173.099(1) MHz) s-cis (A=5207.292(1), B=3470.930(1) C=2113.496(1) MHz). conformation is global minimum, with energy 4(2) kJ mol−1 calculated isomerization barrier 15 mol−1. Except for methyl hydrogen atoms, s-cis-methacrylamide planar its internal rotation 10.2(1) In s-trans-methacrylamide allyl amino frames form dihedral angle about 30° 7.4 This different behaviour explained terms attractive repulsive intramolecular interactions between groups: CH2/CO CH3/NH2 s-cis, CH2/NH2 CH3/CO s-trans. tunneling splitting related double-well potential describing interconversion equivalent forms 837.97(2) MHz reproduced one-dimensional flexible model 3.6 barrier.