CONFORMATIONAL ISOMERISM OF N-BUTYL NITRATE STUDIED BY MICROWAVE SPECTROSCOPY

The rotational spectrum of n-butyl nitrate was measured with a chirped pulse Fourier transform microwave \mbox{spectrometer} over the range of 7-13 GHz. This allowed for the identification and assignment of five conformers, AGA, GAA, GGA, AAA, and GG'A with intensity ratios of approximately 1 : 0.2 : 0.2 : 0.1 : 0.1. These conformers were \mbox{subsequently} investigated by Balle-Flygare Fourier transform microwave spectroscopy in order to resolve the nuclear \mbox{electric} quadruople coupling splitting and for further transitions to be collected, allowing improved fitting. Isotopic \mbox{substitutions} at natural abundance were also observed for the AGA conformer. Quantum chemical calculations reveal that the AGA \mbox{conformer} is the lowest in energy. A variety of computational methods were used to explore the energy ordering and barriers between inter-conversion of the lowest lying energy conformers. This work extends a series of other alkyl nitrate works studied by microwave and mm-wave spectroscopy.\footnote{Methyl Nitrate; W.B. Dixon, E.B. Wilson, {\it{J. Chem. Phys.}}, {\bf{35}}, 191 (1961)} \footnote{Ethyl Nitrate; D.G. Scroggrin, J.M. River, E.B. Wilson, {\it{J. Chem. Phys.}}, {\bf{60}}, 1376 (1974); J. Thomas, I. Medvedev, D. Dolson, ISMS 2014} \footnote{n-Propyl Nitrate; W. Orellana, S.L. Stephens, S.E. Novick, S.A. Cooke, C. Brauer, T.A. Blake, ISMS 2019} \begin{center} \includegraphics[width=0.95\textwidth] {nBN.eps} \end{center

A STUDY OF THE CONFORMATIONAL ISOMERISM OF N-PROPYL NITRATE BY MICROWAVE SPECTROSCOPY

The rotational spectrum of n-propyl nitrate was measured in the frequency range between 6-18 GHz using a Balle-Flygare Fourier transform microwave jet/cavity spectrometer. Parent, $^{13}$C and $^{15}$N isotopologue transitions for the lower-energy anti-gauche (AG) conformer were found using this instrument. The search for spectra from other conformers was performed using a broadband chirped-pulse jet spectrometer. Transitions from the anti-anti (AA) conformer were observed in this manner. Parent, $^{13}$C and $^{15}$N isotopologue transitions for the AA conformer were rescanned using the cavity instrument to improve resolution and the signal-to-noise ratio. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants for all conformers/isotopologues were fit using Pickett’s SPFIT program. The structure of n-propyl nitrate will be discussed in light of these results. \begin{center} \includegraphics[scale=0.6] {PROPYL_NITRATE_1.eps} \end{center

2-METHYl-1-HEXEN-3-YNE AND 3-HEXYN-2-ONE ADVENTURES IN METHYL GROUP INTERNAL ROTATION

The two titled molecules have been studied in the past by one of us (RKB) and coworkers. Due to unassigned splittings of the methyl internal rotations, and inconsistencies in the spectroscopic fits the studies were deemed incomplete for a manuscript but were previously presented in isolation at ISMS in Columbus.\footnote{Microwave study of 2-Methyl-Hexene-3-yne; Ground state and tortionally excited state; Yeager. Joseph, Bohn. Robert.K ISMS 2007}{$^{,}$}\footnote{Rotational spectrum and structure of 3-Hexyn-2-one; Bohn. Robert.K ISMS 1997} By re-measurement we have identified new small splittings and added breadth the spectral fits to allow improved fitting. Parameters characterizing internal rotation have been determined for 2-methyl-1-hexen-3-yne for the first time. This work is part of a larger series of work which attempts to rationalize how molecules undergo structural and dynamical changes when altering one moiety, for example how an environment surrounding a double bond hinders the free rotation of an adjacent methyl group

MICROWAVE SPECTRA AND GEOMETRIES OF C2H2…AgI and C2H4…AgI

A chirped-pulse Fourier transform microwave spectrometer has been used to measure the microwave spectra of both $mathrm{C_{2}H_{2}cdots AgI}$ and $mathrm{C_{2}H_{4}cdots AgI}$. These complexes are generated via laser ablation at 532 nm of a silver surface in the presence of $mathrm{CF_{3}I}$ and either $mathrm{C_{2}H_{2}}$ or $mathrm{C_{2}H_{4}}$ and argon and are stabilized by a supersonic expansion. Rotational ($A_{0}$, $B_{0}$, $C_{0}$) and centrifugal distortion constants ($Delta_{J}$ and $Delta_{JK}$) of each molecule have been determined as well the nuclear electric quadrupole coupling constants the iodine atom ($chi_{aa}left(mathrm{I}right)$ and $chi_{bb}-chi_{cc}left(mathrm{I}right)$). The spectrum of each molecule is consistent with a $C_{2mathrm{v}}$ structure in which the metal atom interacts with the $pi$-orbital of the ethene or ethyne molecule. Isotopic substitutions of atoms within the $mathrm{C_{2}H_{2}}$ or $mathrm{C_{2}H_{4}}$ subunits are in progress and in conjunction with high level textit{ab initio} calculations will allow for accurate determination of the geometry of each molecule. These to complexes are put in the context of the recently studied $mathrm{H_{2}Scdots AgI}$,footnote{S.Z. Riaz, S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, Chem. Phys. Let., $bf{531}$, 1-12 (2012)} OC$cdots$AgI,footnote{S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, J. Chem. Phys., $bf{136(6)}$, 064306 (2012)}, $mathrm{H_{3}Ncdots AgI}$ and $mathrm{left(CH_{3}right)_{3}Ncdots AgI}$.footnote{D.M. Bittner, D.P. Zaleski, S.L. Stephens, N.R. Walker, A.C. Legon, Study in progress.

ROTATIONAL SPECTRA OF 4,4,4-TRIFLUOROBUTYRIC ACID AND THE 4,4,4-TRIFLUOROBUTYRIC ACID-FORMIC ACID COMPLEX

The pure rotational spectra of 4,4,4-trifluorobutyric acid, CF$_3$CH$_2$CH$_2$COOH, and its complex with formic acid, were studied by a pulsed nozzle, chirped-pulse Fourier transform microwave spectrometer in the frequency range of 8-12 GHz. The rotational constants and centrifugal distortion constants were determined for the first time. Quantum chemical calculations were carried out exploring possible conformations of 4,4,4-trifluorobutyric and the structure of the 4,4,4-trifluorobutyric acid-formic acid complex using B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ calculations. The experimental spectroscopic constants are compared to those obtained from $it{ab}$ $it{initio}$ calculations. _x000d

CONFORMATIONAL ISOMERISM OF 1-IODOPENTANE

The rotational spectrum of 1-iodopentane was measured over the 7-13 GHz frequency range with a chirped pulse Fourier transform microwave spectrometer revealing rotational transitions from a number of conformers. \begin{wrapfigure}{l}{0pt} \includegraphics[scale=0.3]{1-Iodopentane_GAA.eps} \end{wrapfigure} This continues the group's work on how a large substituent, in this case an iodine atom, at the terminal position will affect the dihedral angles of the alkyl carbon backbone and what influence it will exert with continuing chain length. In keeping with last year’s study of 1-iodobutane,\footnote{Arsenault E.A.; Obenchain, D.A.; Blake, T.A.; Cooke, S.A.; Novick, S.E; {\it{J. Mol. Spectrosc.}}, {\bf{2017}} {\it{335}} 17-22.} we find that the corresponding GAA conformer is the most abundant, and that while the nuclear quadrupole coupling tensor is poorly predicted by direct {\it{ab initio}} methods, scaling methods\footnote{Anticipated future communication with W. C. Bailey.} allow very reasonable predictions to be obtained

H₃P⋯AgI:Generation by laser-ablation and characterization by rotational spectroscopy and: Ab initio calculations

The new compound H(3)P···AgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF(3) and PH(3) in argon. Ground-state rotational spectra were detected and assigned for the two isotopologues H(3)P···(107)AgI and H(3)P···(109)AgI in their natural abundance by means of a chirped-pulse, Fourier-transform, microwave spectrometer. Both isotopologues exhibit rotational spectra of the symmetric-top type, analysis of which led to accurate values of the rotational constant B (0), the quartic centrifugal distortion constants D (J) and D (JK), and the iodine nuclear quadrupole coupling constant χ (aa)(I) = eQq (aa). Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12*)/aug-cc-pVDZ confirmed that the atoms P···Ag–I lie on the C (3) axis in that order. The experimental rotational constants were interpreted to give the bond lengths r (0)(P···Ag) = 2.3488(20) Å and r (0)(Ag–I) = 2.5483(1) Å, in good agreement with the equilibrium lengths of 2.3387 Å and 2.5537 Å, respectively, obtained in the ab initio calculations. Measures of the strength of the interaction of PH(3) and AgI (the dissociation energy D (e) for the process H(3)P···AgI = H(3)P + AgI and the intermolecular stretching force constant F (P···Ag)) are presented and are interpreted to show that the order of binding strength is H(3)P···HI < H(3)P···ICl < H(3)P···AgI for these metal-bonded molecules and their halogen-bonded and hydrogen-bonded analogues

Gas phase complexes of H₃N⋯CuF and H₃N⋯CuI studied by rotational spectroscopy and:Ab initio calculations: The effect of X (X = F, Cl, Br, I) in OC⋯CuX and H₃N⋯CuX

Complexes of H3N⋯CuF and H3N⋯CuI have been synthesised in the gas phase and characterized by microwave spectroscopy.</p

Mutational processes molding the genomes of 21 breast cancers

All cancers carry somatic mutations. The patterns of mutation in cancer genomes reflect the DNA damage and repair processes to which cancer cells and their precursors have been exposed. To explore these mechanisms further, we generated catalogs of somatic mutation from 21 breast cancers and applied mathematical methods to extract mutational signatures of the underlying processes. Multiple distinct single- and double-nucleotide substitution signatures were discernible. Cancers with BRCA1 or BRCA2 mutations exhibited a characteristic combination of substitution mutation signatures and a distinctive profile of deletions. Complex relationships between somatic mutation prevalence and transcription were detected. A remarkable phenomenon of localized hypermutation, termed "kataegis," was observed. Regions of kataegis differed between cancers but usually colocalized with somatic rearrangements. Base substitutions in these regions were almost exclusively of cytosine at TpC dinucleotides. The mechanisms underlying most of these mutational signatures are unknown. However, a role for the APOBEC family of cytidine deaminases is proposed