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This work presents the results of kinetic measurements for the reactions of atomic bromine with the three isomers of trimethylbenzene at temperatures from 295 K to 354 K and at pressures close to atmospheric. The atomic bromine was produced by photolysis of Br 2 in a thermostated Pyrex chamber as described in our previous work. The reactants were present as dilute mixtures in argon with Br 2 in sufficient excess to scavenge the free radical products of the initiation step. Chemical analysis was by gas chromatography and the rate coefficients were calculated from the chromatographic results using the relative rate method. The experimentally measured temperature dependence of the rate coefficients for the reactions of Br with the trimethylbenzenes is given in the units cm 3 molec. -1 s -1 by: 1,2,3-trimethylbenzene + Br, log 10 ( k ) = -9.57 ± 0.43 - (996 ± 134)/ T ; 1,2,4-trimethylbenzene + Br, log 10 ( k ) = -9.74 ± 0.29 - (968 ± 91)/ T ; 1,3,5-trimethylbenzene + Br, log 10 ( k ) = -9.87 ± 0.26 - (1079 ± 85)/ T . The enthalpies and entropies of activation for these reactions are compared to those for the reactions of Br with toluene and the xylenes.

Population genetic studies of North Asian ethnic groups have focused on genetic variation of sex chromosomes and mitochondria. Studies of the extensive variation available from autosomal variation have appeared infrequently. We focus on relationships among population samples using new North Asia microhaplotype data. We combined genotypes from our laboratory on 58 microhaplotypes, distributed across 18 autosomes, on 3945 individuals from 75 populations with corresponding data extracted for 26 populations from the Thousand Genomes consortium and for 22 populations from the GenomeAsia 100 K project. A total of 7107 individuals in 122 total populations are analyzed using STRUCTURE, Principal Component Analysis, and phylogenetic tree analyses. North Asia populations sampled in Mongolia include: Buryats, Mongolians, Altai Kazakhs, and Tsaatans. Available Siberians include samples of Yakut, Khanty, and Komi Zyriane. Analyses of all 122 populations confirm many known relationships and show that most populations from North Asia form a cluster distinct from all other groups. Refinement of analyses on smaller subsets of populations reinforces the distinctiveness of North Asia and shows that the North Asia cluster identifies a region that is ancestral to Native Americans., (© 2022. The Author(s).)

This work reports the temperature dependence of the rate coefficients for the reactions of atomic bromine with the xylenes that are determined experimentally and theoretically. The experiments were carried out in a Pyrex chamber equipped with fluorescent lamps to measure the rate coefficients at temperatures from 295 K to 346 K. Experiments were made at several concentrations of oxygen to assess its potential kinetic role under atmospheric conditions and to validate comparison of our rate coefficients with those obtained by others using air as the diluent. Br 2 was used to generate Br atoms photolytically. The relative rate method was used to obtain the rate coefficients for the reactions of Br atoms with the xylenes. The reactions of Br with both toluene and diethyl ether (DEE) were used as reference reactions where the loss of the organic reactants was measured by gas chromatography. The rate coefficient for the reaction of Br with diethyl ether was also measured in the same way over the same temperature range with toluene as the reference reactant. The rate coefficients were independent of the concentration of O 2 . The experimentally determined temperature dependence of the rate coefficients of these reactions can be given in the units cm 3 molecule -1 s -1 by: o -xylene + Br, log 10 ( k ) = (-10.03 ± 0.35) - (921 ± 110)/ T ; m -xylene + Br, log 10 ( k ) = (-10.78 ± 0.09) - (787 ± 92/ T ); p -xylene + Br, log 10 ( k ) = (-9.98 ± 0.39) - (956 ± 121)/ T ; diethyl ether + Br, log 10 ( k ) = (-7.69 ± 0.55) - (1700 ± 180)/ T ). This leads to the following rate coefficients, in the units of cm 3 molecule -1 s -1 , based on our experimental measurements: o -xylene + Br, k (298 K) = 7.53 × 10 -14 ; m -xylene + Br, k (298 K) = 3.77 × 10 -14 ; p -xylene + Br, k (298 K) = 6.43 × 10 -14 ; diethyl ether + Br, k (298 K) = 4.02 × 10 -14 . Various ab initio methods including G3, G4, CCSD(T)/cc-pV(D,T)Z//MP2/aug-cc-pVDZ and CCSD(T)/cc-pV(D,T)Z//B3LYP/cc-pVTZ levels of theory were employed to gain detailed information about the kinetics as well as the thermochemical quantities. Among the ab initio methods, the G4 method performed remarkably well in describing the kinetics and thermochemistry of the xylenes + Br reaction system. Our theoretical calculations revealed that the reaction of Br atoms with the xylenes proceeds via a complex forming mechanism in an overall endothermic reaction. The rate determining step is the intramolecular rearrangement of the pre-reactive complex leading to the post-reactive complex. After lowering the relative energy of the corresponding transition state by less than 1.5 kJ mol -1 for this step in the reaction of each of the xylenes with Br, the calculated rate coefficients are in very good agreement with the experimental data.