The current state of ab initio calculations of optical rotation and electronic circular dichroism spectra.

The current ability of ab initio models to compute chiroptical properties such as optical rotatory dispersion and electronic circular dichroism spectra is reviewed. Comparison between coupled cluster linear response theory and experimental data (both gas and liquid phase) yields encouraging results for small to medium-sized chiral molecules including rigid species such as (S)-2-chloropropionitrile and (P)-[4]triangulane, as well as conformationally flexible molecules such as (R)-epichlorohydrin. More problematic comparisons are offered by (S)-methyloxirane, (S)-methylthiirane, and (1S,4S)-norbornenone, for which the comparison between theory and experiment is much poorer.

Chiroptical properties of (R)-3-chloro-1-butene and (R)-2-chlorobutane.

Coupled cluster and density functional models of specific rotation and vacuum UV (VUV) absorption and circular dichroism spectra are reported for the conformationally flexible molecules (R)-3-chloro-1-butene and (R)-2-chlorobutane. Coupled cluster length- and modified-velocity-gauge representations of the Rosenfeld optical activity tensor yield significantly different specific rotations for (R)-3-chloro-1-butene, with the latter providing much closer comparison (within 3%) to the available gas-phase experimental data at 355 and 633 nm. Density functional theory overestimates the experimental rotations for (R)-3-chloro-1-butene by approximately 80%.

Ab initio determination of optical rotatory dispersion in the conformationally flexible molecule (R)-epichlorohydrin.

Ab initio optical rotation data from linear-response coupled-cluster and density-functional methods are compared to both gas-phase and liquid-phase polarimetry data for the small, conformationally flexible molecule epichlorohydrin. Three energy minima exist along the C-C-C-Cl dihedral angle, each with strong, antagonistic specific rotations ranging from ca. -450 to +500 deg/[dm (g/mL)] at 355 nm.

Ab initio calculation of optical rotation in (P)-(+)-[4]triangulane.

Optical rotation, the angle through which plane-polarized light rotates when passed through an enantiomerically pure medium, plays a vital role in the determination of the absolute configurations of chiral molecules such as natural products. We describe new quantum mechanical methodology designed to assist in this endeavor by providing high-accuracy computational optical rotatory dispersion data for matching to experimental results. Comparison between theory and experiment for the rigid, helical molecule trispiro[2.

A family of decamethylmetallocene charge-transfer salt magnets using methyl tricyanoethylenecarboxylate (MTCE) as the electron acceptor.

Methyl tricyanoethylenecarboxylate, MTCE, has been used as a one-electron acceptor building block for the synthesis of isomorphous decamethylmetallocene charge-transfer salt magnets of the formula [MCp*2][MTCE], M = Cr, Mn, and Fe. Functionally and electrochemically, MTCE is a hybrid between tetracyanoethylene (TCNE) and dimethyl dicyanofumarate (DMeDCF), two acceptors that have previously been found to support ferromagnetism. The X-ray crystal structure of the chromium analogue, [CrCp*2][MTCE], shows it to exist in the expected mixed stack structure in the orthorhombic space group Pnma with a = 14.

Coupled cluster calculations of optical rotatory dispersion of (S)-methyloxirane.

Coupled cluster (CC) and density-functional theory (DFT) calculations of optical rotation, [alpha](lambda), have been carried out for the difficult case of (S)-methyloxirane for comparison to recently published gas-phase cavity ringdown polarimetry data. Both theoretical methods are exquisitely sensitive to the choice of one-electron basis set, and diffuse functions have a particularly large impact on the computed values of [alpha](lambda). Furthermore, both methods show a surprising sensitivity to the choice of optimized geometry, with [alpha](355) values varying by as much as 15 deg dm(-1) (g/mL)(-1) among molecular structures that differ only negligibly.