The rotational spectra of N-, 2-, 4-, and 5-methylimidazole are reported and analyzed. Liquid N-methylimidazole was vaporized from a reservoir, and each of 2-, 4-, and 5-methylimidazole was laser-vaporized from a solid target prior to mixing with argon buffer gas and undergoing supersonic expansion from a pulsed nozzle. The spectra were recorded by chirped-pulse Fourier transform microwave spectroscopy in the 7.0–18.5 GHz frequency range. Rotational constants, A0, B0, and C0, centrifugal distortion constants, DJ, DJK, DK, d1, and d2, and nuclear quadrupole coupling constants of nitrogen atoms, χaa(N1), χbb(N1) − χcc(N1), χaa(N3), and χbb(N3) − χcc(N3), are determined from experimentally measured transition frequencies. Data recorded for isotopologues containing 13C or 15N are used to determine the rs coordinates of all heavy atoms in N-, 2-, and 4-methylimidazole. The results allow fitting of parameters in the Hamiltonian that describes internal rotation of the CH3 group about its local C3 axis. The V3 terms in the periodic potential energy functions that describe the internal rotation in N-, 2-, 4-, and 5-methylimidazole are determined to be 185.104(11), 122.7529(38), 317.20(14), and 386.001(19) cm−1, respectively, by the internal axis method. The experiments are supported by density functional theory calculations. Observed variations in barrier height are explained with reference to the symmetry of overlap between a π-like orbital on the CH3 group and π-orbitals on the aromatic ring.

Enantiopure secondary alcohols are fundamental high-value synthetic building blocks.One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe an ew concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule.C ontrol experiments reveal that both catalytic centers are essential for the observed activity.Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via ac oncerted mechanism, in whichh ydride at Boron is continuously displaced by iodide,r eminiscent to an S N 2r eaction. The catalyst, whichi s accessible in high yields in few steps,w as found to be stable during catalysis,r eadily recyclable and could be reused 10 times still efficiently working.

Broadband microwave spectra have been recorded between 7.0 and 18.5 GHz for N-methylimidazole…H2O and 2-methylimidazole…H2O complexes. Each complex was generated by co-expansion of low concentrations of methylimidazole and H2O in...

In memory of Klaus HafnerAzulene is stabilized by "zwitterionic aromaticity", what about its ring carbo-mer? The greater dipole moment of the latter is oriented in the opposite direction, while providing an enhanced zwitterionic aromatic character. Comparison of local aromaticity indices for the two rings, with 5 and 7 CÀ C bonds in azulene or CÀ C 2 À C edges in carbo-azulene, allows analysis of the quasiindependent influence of size on the π-electronic properties of these aromatic bicyclic molecules exhibiting quasi-identical shapes and π-resonance schemes between their common set of sp 2 CÀ H vertices. The electrostatic features of such dipolar hydrocarbons are also analyzed by comparison with their respective radical cation and anion, and with their apolar bicyclic isomer, naphthalene and carbo-naphthalene.