Microwave Spectra and Molecular Structures of (Z)-Pent-2-en-4-ynenitrile and Maleonitrile

Abstract

Accurate equilibrium structures have been determined for (Z)-pent-2-en-4-ynenitrile (8) and maleonitrile (9) by combining microwave spectroscopy data and ab initio quantum chemistry calculations. The microwave spectra of 10 isotopomers of 8 and 5 isotopomers of 9 were obtained using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants were adjusted for vibration-rotation interaction effects calculated from force fields obtained from ab initio calculations. The resultant equilibrium rotational constants were used to determine structures that are in very good agreement with those obtained from high-level ab initio calculations (CCSD(T)/cc-pVTZ). The geometric parameters in 8 and 9 are very similar; they also do not differ significantly from the all-carbon analogue, (Z)-hex-3-ene-1,5-diyne (7), the parent molecule for the Bergman cyclization. A small deviation from linearity about the alkyne and cyano linkages is observed for 7-9 and several related species where accurate equilibrium parameters are available. The data on 7-9 should be of interest to radioastronomy and may provide insights on the formation and interstellar chemistry of unsaturated species such as the cyanopolyynes.

The bergman cyclizations of the enediyne and its N‐substituted analogs using multiconfigurational second‐order perturbation theory

“…[25]. [1,7,19] Similar to the situation of 1R, both 2R t (2R in the T 1 state) and 3R t (3R in the T 1 state) have lower symmetry (C 1 symmetry) than their respective S 0 states. The CASPT2 geometry of 2R s is in good agreement with experiment (see Fig.…”

“…Halter et al [1] performed the geometry optimization calculations for 2R and 4R in their ground states (the S 0 states) using CCSD(T)/cc-pVTZ method and the optimized geometries are in agreement with experiment. For the Bergman cyclizations of 2R and 3R (reactions 2 and 3 in Scheme 1), there are a few theoretical studies [1,7,19,22,[36][37][38] reported in the literature.…”

“…Halter et al [1] performed the geometry optimization calculations for 2R and 4R in their ground states (the S 0 states) using CCSD(T)/cc-pVTZ method and the optimized geometries are in agreement with experiment. For the Bergman cyclizations of 2R and 3R (reactions 2 and 3 in Scheme 1), there are a few theoretical studies [1,7,19,22,[36][37][38] reported in the literature. Hoffner et al [22] studied these two reactions along the S 0 potential energy surfaces (PESs) by performing the CASSCF(6,6)/6-31G* and CASMP2(6,6)/6-31G* single-point energy calculations at the CASSCF(6,6)/3-21G geometries and predicted the energy barriers, the reaction enthalpies, and the singlet-triplet splitting for the biradical products.…”

“…[1] In addition, the enediyne-like structure is an important moiety of potent anti-tumor antibiotics such as calicheamicin, dynemicin, and esperamicin and has been shown to produce the highly reactive biradical, which was found to be responsible for the activity of the enediyne class antitumor antibiotics. [2][3][4][5][6][7] Due to the high cytotoxicity of enediynes to normal cells, [2] the analogs with one carbon atom replaced by one nitrogen atom were considered as the best candidate for a new enediyne anticancer drug.…”

“…The experimental geometric data for 2R and 4R were reported by Halter et al, [1] but neither experimental geometric data for 3R and 5R nor experimental thermodynamic data for reactions 2-5 are available in the literature. Hoffner et al [22] and Cramer [19] calculated the ground state geometries of 2R…”