ChemInform Abstract: Molecular Structure and Conformation of 2,4‐Dimethylpentane Studied by Gas Electron Diffraction Combined with Vibrational Spectroscopy and ab initio Calculation.

Abstract

Abstract The molecular structure of 2,4-dimethylpentane has been studied by gas electron diffraction with the aid of vibrational spectroscopy and ab initio calculations on the 4–21G level. The most stable conformer has C2 symmetry, whereas the next most stable conformer has C1 symmetry with the dihedral angles of o1(C5C1C2H8)=20° and o2(C2C1C5H9)= 179°. The populations of the C2 and C1 conformers at 24°C are found to be 90(5)% and 10(5)%, respectively. The structural parameter values of the C2 conformer are as follows: rg (C1–C2)=1.539(2) A, rg(C2–C3)=1.534 A, rg(C2–C4)=1.535 A, rg(CH)av=1.119(2) A, ∠αC2C1C5=117.8(6)°, ∠αC1C2C3=111.5(8)°, ∠αC1C2C4=109.9(4)°, ∠αC3C2C4=111.5(8)°, ∠αCCHMe=111.0(7)°, and o1 (=o2) =57.5(17)°. The experimental structural parameter values are in good agreement with the theoretical ones. However, the 4–21G calculations predict that the C1 (o1=25°, o2=−59°) form is more stable than the C1 (o1=20°, o2=179°) form. The results are compared with the structures of related compounds.