15min:

NORMAN C. CRAIG AND HENGFENG TIAN, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; THOMAS A. BLAKE, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352.

Hexatriene-1-¹³ C ₁ was synthesized by reaction of 2,4-pentadienal and (methyl-¹³ C )-triphenylphosphonium iodide (Wittig reagent). The trans isomer was isolated by preparative gas chromatography, and the high-resolution (0.0015 cm^-1) infrared spectrum was recorded on a Bruker IFS 125HR instrument. The rotational structure in two C-type bands was analyzed. For this species the bands at 1010.7 and 893.740 cm^-1 yielded composite ground state rotational constants of A ₀ = 0.872820(1), B ₀ = 0.0435868(4), and C ₀ = 0.0415314(2) cm^-1. The ground state rotational constants for the 1-¹³C species were also predicted with Gaussian 03 software and the B3LYP/cc-pVTZ model. After scaling by the ratio of the observed and predicted ground state rotational constants for the normal species, the predicted ground state rotational constants for the 1-¹³C species agreed within 0.005 % with the observed values. Similar good agreement between observed and calculated values (0.016 %) was found for the three ¹³C species of the cis isomer. We conclude that ground state rotational constants for single heavy atom substitution can be calculated with adequate accuracy for use in determining semi-experimental equilibrium structures of small molecules. It will be unnecessary to synthesize the other two ¹³C species of trans -hexatriene.