Benzvalyne: Real or imaginary?

Benzvalyne (CH) is a bicyclic structural isomer of o-benzyne that some typically trusted levels of theory do not report as a minimum on the potential energy surface (PES). The structure was found to be a C minimum at the MCSCF, MP2, coupled-cluster single double, coupled-cluster single double triple (CCSDT)-1b, and CCSDT-2 levels of theory. Density functionals at the B3LYP-D3, B2PLYP-D3, and M06-D3 levels also produced a minimum structure.

Noncovalent Interactions between Trimethylamine N-Oxide (TMAO), Urea, and Water.

Trimethylamine N-oxide (TMAO) and urea are two important osmolytes with their main significance to the biophysical field being in how they uniquely interact with proteins. Urea is a strong protein destabilizing agent, whereas TMAO is known to counteract urea's deleterious effects. The exact mechanisms by which TMAO stabilizes and urea destabilizes folded proteins continue to be debated in the literature.

Noncovalent interactions in microsolvated networks of trimethylamine N-oxide.

The effects of the formation of hydrogen-bonded networks on the important osmolyte trimethylamine N-oxide (TMAO) are explored in a joint Raman spectroscopic and electronic structure theory study. Spectral shifts in the experimental Raman spectra of TMAO and deuterated TMAO microsolvated with water, methanol, ethanol, and ethylene glycol are compared with the results of electronic structure calculations on explicit hydrogen-bonded molecular clusters. Very good agreement between experiment and theory suggests that it is the local hydrogen-bonded geometry at TMAO's oxygen atom that dominates the structure of the extended hydrogen-bonded networks and that TMAO's unique stabilizing abilities are a result of the "indirect effect" model.

Conventional strain energies of azetidine and phosphetane: can density functional theory yield reliable results?

The conventional strain energies for azetidine and phosphetane are determined within the isodesmic, homodesmotic, and hyperhomodesmotic models. Optimum equilibrium geometries, harmonic vibrational frequencies, and corresponding electronic energies and zero-point vibrational energies are computed for all pertinent molecular systems using self-consistent field theory, second-order perturbation theory, and density functional theory and using the correlation consistent basis sets cc-pVDZ, cc-pVTZ, and cc-pVQZ. Single point fourth-order perturbation theory, CCSD, and CCSD(T) calculations using the cc-pVTZ and the cc-pVQZ basis sets are computed using the MP2/cc-pVTZ and MP2/cc-pVQZ optimized geometries, respectively, to ascertain the contribution of higher order correlation effects and to determine if the quadruple-zeta valence basis set is needed when higher order correlation is included.

Raman spectroscopic signatures of noncovalent interactions between trimethylamine N-oxide (TMAO) and water.

The effects of hydration on vibrational normal modes of trimethylamine N-oxide (TMAO) are investigated by Raman spectroscopy and electronic structure computations. Microsolvated networks of water are observed to induce either red or blue shifts in the normal modes of TMAO with increasing water concentration and to also exhibit distinct spectral signatures. By taking advantage of the selective and gradual nature of the water-induced shifts and using comparisons to theoretical predictions, the assignments of TMAO's normal modes are re-examined and the structure of the hydrogen-bonded network in the vicinity of TMAO is elucidated.

Conventional strain energy in dimethyl-substituted cyclobutane and the gem-dimethyl effect.

The gem-dimethyl effect is the acceleration of cyclization by substituents in the chain and is often used in organic synthesis as a ring-closing effect. Calculations on cyclobutane, methylcyclobutane, and 1,1-dimethylcyclobutane are performed. 1,1-Dimethylcyclobutane is a four-membered carbon ring with gem-dimethyl substituents.

Stability and thermal rearrangement of (E,E)-1,3-cycloheptadiene and trans-bicyclo[3.2.0]hept-6-ene.

The highly strained (E,E)-1,3-cycloheptadiene was shown to be a minimum on the potential energy surface; two structural isomers were found at the MP2 level, but multiconfiguration self-consistent field calculations show that only one is a true minimum. The isomerization of (E,E)-1,3-cycloheptadiene was investigated through double bond rotation, and electrocyclic ring closure. The first pathway gives (E,Z)-1,3-cycloheptadiene, with a barrier of 7.