Optical Rotatory Dispersion of 2,3-Hexadiene and 2,3-Pentadiene

Abstract

The specific rotation of (P)-2,3-hexadiene (1) was measured as a function of wavelength for the gas phase, the neat liquid, and solutions. There was a surprisingly large difference between the gas phase and condensed phase values. The specific rotation was calculated using B3LYP and CCSD, and the difference in energy between the three low energy conformers was estimated at the G3 level. The Boltzmann-averaged CCSD-calculated rotations using the gauge independent velocity gauge representation, as well as the B3LYP values, are in agreement with the gas-phase experimental values. In order to avoid possible problems associated with the conformers of 1, 2,3-pentadiene (2) also was examined. Here again, there was a large difference between the gas-phase and condensed-phase specific rotations, with the CCSD velocity gauge (and B3LYP) results being close to the gas-phase experimental values. The possibility that 2,3-pentadiene could be distorted on going from the gas to liquid phase, thereby accounting for the effect of phase on the specific rotation, was examined via a Monte Carlo statistical mechanics simulation. No effect on the geometry was found. Specific rotations of 1 found in solutions were similar to those for the liquid phase, indicating that the phase difference was not due to association.

Gas phase optical rotation calculated from coupled cluster theory with zero‐point vibrational corrections from density functional theory

“…[27][28][29][30] For conformationally flexible molecules, a simple Boltzmann procedure has been applied to average the electronic contributions from different conformations. 5,25,[31][32][33][34][35][36][37][38] Comparing to a rigorous vibrational averaging procedure involving all conformations of 3-chloro-1-butene, Crawford and Allen 26 have shown that the simple approach benefits from cancellation of errors. Solvent effects on optical rotations have been modeled by means of continuum methods, both with 20,39 and without 14,28 vibrational contributions.…”

Towards the Accurate and Efficient Calculation of Optical Rotatory Dispersion Using Augmented Minimal Basis Sets

“…The ( P ) ‐ (+) ‐ 2, 3 ‐ pentadiene system represents another example of a chiral molecule where theoretical predictions of dispersive optical activity differ markedly from laboratory results obtained under isolated (vapor‐phase) conditions . As shown by Table , DFT(B3LYP) linear‐response analyses performed with the canonical aug‐cc ‐ pVDZ and aug‐cc ‐ pVTZ bases are in reasonable accord with one another, yet depart from the intrinsic behavior measured at 355 nm and 633 nm by − 29.1% and − 12.5%, respectively, for the triple ‐ ζ form.…”

“…Coupled‐cluster methods improve on this situation (cf., Table ), with CCSD(MVG)/aug‐cc ‐ pVDZ calculations reducing the deviations between experiment and theory to − 9.2% and − 10.4% for the two excitation wavelengths. It should be noted that an unusually large difference in specific‐rotation values exists for 5 between solution‐phase and vapor‐phase environments …”

“…The ensuing analyses have focused on five nominally rigid chiral molecules, most of which have known intrinsic (gas‐phase) specific rotations measured at 355 nm and 633 nm through the use of ultrasensitive cavity ring‐down polarimetry . As shown in Figure , the species targeted by the present investigation are ( S ) ‐ (+) ‐ 3 ‐ carene ( 1 ), (1 S , 5 S ) ‐ (−) ‐ α ‐ pinene ( 2 ), (1 R , 2 S , 5 R ) ‐ (+) ‐ cis‐pinane ( 3 ), ( S ) ‐ (−) ‐ norbornenone ( 4 ), and ( P ) − (+) ‐ 2, 3 ‐ pentadiene ( 5 ) . This represents a diverse set of organic compounds, both in terms of chemical functionalities and physiochemical properties, with some members displaying features of particular interest for studies of dispersive chiroptical phenomena.…”

“…This represents a diverse set of organic compounds, both in terms of chemical functionalities and physiochemical properties, with some members displaying features of particular interest for studies of dispersive chiroptical phenomena. For example, the extrapolated sodium D − line (589.3 nm) specific rotation of 5 in the vapor phase, , is almost twice as large as the attendant liquid‐phase parameter of + 81 deg dm − 1 (g/mL) − 1 . On the other hand, the intrinsic rotatory power of 4 estimated by CCSD linear‐response analyses, [ α ] D = − 550 deg dm − 1 (g/mL) − 1 , is nearly a factor of 2 smaller in magnitude than published solution‐phase measurements, which straddle − 1000 deg dm − 1 (g/mL) − 1 for a variety of solvents and are reproduced somewhat better within the framework of density‐functional theory .…”