Knowledge Bank

We seek a semi-experimental equilibrium structure for {\em trans}-1,3,5-hextatriene, which should show structural evidence for increased pi-electron delocalization in comparison with butadiene. Despite the marginal resolution in the spectrum of {\em trans}-hexatriene, rotational structure of three C-type bands of trans-hexatriene in the high-resolution infrared spectrum (0.0015 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) has been analyzed as a first step. Strong bands are at 1010.95 and 901.910 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$; a weaker band is at 683.45 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. The most extensive analysis was for the band at 901.910 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. The composite fit of 1628 ground state combination differences from the three bands gave the ground state rotational constants of {\em A} = 0.8742480(7), {\em B} = 0.0446600(10), and {\em C} = 0.0425099(8) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. For this near-symmetric top, $\kappa$ = -0.99483. Procedures for synthesizing needed isotopomers are being explored.