TY - JOUR
T1 - Microwave spectroscopy and structures of two conformers of 6-methyl-3-heptyne and three of 2-methylpentane
AU - Fournier, Joseph A.
AU - Bohn, Robert K.
AU - Michels, H. Harvey
PY - 2008/9
Y1 - 2008/9
N2 - From its microwave rotational spectrum, 6-methyl-3-heptyne (MHept, ethyl isobutyl acetylene) has been characterized in two conformations of Cs and C1 symmetry with the opposing alkyl groups arranged syn-eclipsed or nearly so about the C{triple bond, long}C axis. The dominant interaction determining the dihedral angle about the C{triple bond, long}C axis is the small dispersion attraction between the separated ethyl and isobutyl groups. The three lowest energy conformers of 2-methylpentane (MPane), MHept without C{triple bond, long}C, have been characterized from their microwave spectra. MPane has more conformations than MHept because the C3{single bond}C4 bond in MPane has a substantial ethane-like barrier supporting gauche and anti conformations while MHept's tiny C2{single bond}(C3{triple bond, long}C4){single bond}C5 torsional barrier has only a single minimum. Ab initio calculations of both compounds at the MP2/6-311+G(d,p) level agree with the experimental results.
AB - From its microwave rotational spectrum, 6-methyl-3-heptyne (MHept, ethyl isobutyl acetylene) has been characterized in two conformations of Cs and C1 symmetry with the opposing alkyl groups arranged syn-eclipsed or nearly so about the C{triple bond, long}C axis. The dominant interaction determining the dihedral angle about the C{triple bond, long}C axis is the small dispersion attraction between the separated ethyl and isobutyl groups. The three lowest energy conformers of 2-methylpentane (MPane), MHept without C{triple bond, long}C, have been characterized from their microwave spectra. MPane has more conformations than MHept because the C3{single bond}C4 bond in MPane has a substantial ethane-like barrier supporting gauche and anti conformations while MHept's tiny C2{single bond}(C3{triple bond, long}C4){single bond}C5 torsional barrier has only a single minimum. Ab initio calculations of both compounds at the MP2/6-311+G(d,p) level agree with the experimental results.
KW - 2-Methylpentane
KW - 6-Methyl-3-heptyne
KW - Ab initio calculations
KW - Conformational analysis
KW - Microwave spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=50249115591&partnerID=8YFLogxK
U2 - 10.1016/j.jms.2008.02.007
DO - 10.1016/j.jms.2008.02.007
M3 - Article
AN - SCOPUS:50249115591
SN - 0022-2852
VL - 251
SP - 145
EP - 152
JO - Journal of Molecular Spectroscopy
JF - Journal of Molecular Spectroscopy
IS - 1-2
ER -