Torsional splitting and the four-fold barrier to internal rotation: The rotational spectra of vinylsulfur pentafluoride.

Vinylsulfur pentafluoride (VSPF), a molecule with a four-fold internal rotor, -SF4, has been studied with high resolution Fourier transform microwave spectroscopy. We believe that this is the first report of resolved four-fold internal rotation. As such, we have presented the tools needed to understand and analyze such a problem. These include debugging the ERHAM computer program necessary to fit the spectra and the free rotor to high barrier correlation diagram necessary to understand the torsional states of the four-fold rotor. The A, E, and B torsional state rotational transitions are well resolved and assigned. Spectroscopic transitions of four isotopologues of VSPF, H2C=CH-SF5, the normal isotopologue, and the singly substituted 34S and 13C isotopologues were measured and assigned. Contrary to expectation, the A torsional state could not be fit with only a semi-rigid Hamiltonian. The barrier to internal rotation, V 4, is found to be 227 cm-1. Ab initio calculations at the MP2 aug-cc-pVQZ level of theory and basis set were performed and the results of this calculation are compared to our experimental results.

Microwave Spectra, Structure, and Ring-Puckering Vibration of Octafluorocyclopentene.

The rotational spectra of octafluorocyclopentene (C5F8) has been measured for the first time using pulsed jet Fourier transform microwave spectroscopy in a frequency range of 6 to 16 GHz. As in the molecule cyclopentene, the carbon ring is nonplanar, and inversion through the plane results in an inversion pair of ground state vibrational energy levels with an inversion splitting of 18.4 MHz. This large amplitude motion leads to the vibration-rotation coupling of energy levels. The symmetric double minimum ring-puckering potential function was calculated, resulting in a barrier of 222 cm-1. The rotational constants A0 = 962.9590(1) MHz, B0 = 885.1643(4) MHz, C0 = 616.9523(4) MHz, A1 = 962.9590(1) MHz, B1 = 885.1643(4) MHz, C1 = 616.9528(4) MHz, and two centrifugal distortion constants for each state were determined for the parent species and all 13C isotopologues. A mixed coordinate molecular structure was determined from a least-squares fit of the ground state rotational constants of the parent and each 13C isotopologue combined with the equilibrium bond lengths and angles from quantum chemical calculations.

A Study of 2-Iodobutane by Rotational Spectroscopy.

Rotational transitions belonging to 2-iodobutane (sec-butyl-iodide, CH3CHICH2CH3) were measured over the frequency range 5.5-16.5 GHz via jet-pulsed Fourier transform microwave spectroscopy. The complete nuclear quadrupole coupling tensor of iodine, χ, was obtained for the gauche (g)-, anti (a)-, and gauche' (g')-conformers as well as the four (13)C isotopologues of the gauche species. Rotational constants, centrifugal distortion constants, quadrupole coupling constants, and nuclear spin-rotation constants were determined for each species. Changes in χ of the iodine nucleus, resulting from conformational and isotopic differences, are discussed. Isotopic substitution of g-2-iodobutane allowed for an rs structure to be determined for the carbon backbone. Additionally, isotopic substitution in conjunction with an ab initio structure allowed for a fit of various r0 structural parameters belonging to g-2-iodobutane.

A Study of the Monohydrate and Dihydrate Complexes of Perfluoropropionic Acid Using Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectroscopy.

This work reports the first known spectroscopic observation of the monohydrate and dihydrate complexes of perfluoropropionic acid (PFPA). The spectra have been observed using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer in the 7750 to 14,250 MHz region. The structures of the species have been confirmed with the aid of ab initio quantum chemical calculations. Rotational constants A, B, and C have been determined and reported for both species along with centrifugal distortion constants ΔJ, ΔJK, ΔK, δJ, δK for H2O-PFPA and ΔJ, ΔJK, and δJ for (H2O)2-PFPA. Effects due to large amplitude motions were not observable in these experiments. Structures of the complexes have been determined using a combination of experimental second moment values and ab initio results. The complexation of the -OH of one or two water molecules has been found to occur in the plane of the carboxylic acid group forming a six- or eight-member ring.

Bis-trifluoromethyl effect: doubled transitions in the rotational spectra of hexafluoroisobutene, (CF3)2C═CH2.

Rotational spectra for hexafluoroisobutene, and its (13)C isotopologues, have been recorded between 8 and 16 GHz using a chirped pulse, Fourier transform microwave spectrometer. Notably, all spectra observed are doubled with separations between the doublets being between 1 and 60 MHz. We propose that the bis-trifluoromethyl groups of the target molecule are staggered in the equilibrium configuration, and that a novel, out-of-phase rotation through a F-CCC-F planar configuration with low barrier (<100 cm(-1)), leads to the observed doubled rotational spectra.

Structure and barrier to methyl group internal rotation for (CF3)2CFCF2OCH3 and its isomer n-C4F9OCH3 (HFE-7100).

The hydrofluoroether C(4)F(9)OCH(3) (methoxynonafluorobutane, HFE-7100) has been studied by chirped pulse Fourier transform microwave spectroscopy as vapor from the liquid participates in a supersonic expansion of argon. Two isomers are present, (CF(3))(2)CFCF(2)OCH(3) and n-C(4)F(9)OCH(3), and in each case the rotational spectra of only one, dominating, conformer has been assigned. Rotational constants, centrifugal distortion constants, and barriers to methyl group internal rotation for the observed species have been experimentally determined for the first time. We note that Ray's asymmetry parameter for the (CF(3))(2)CFCF(2)OCH(3) isomer is 0.007 083(1), indicating almost "perfect" asymmetry. Also, electronic structure calculations show an extremely short C(frame)-O ether bond length of 1.337 Å.

Some geometric and electronic structural effects of perfluorinating propionyl chloride.

Propionyl chloride and perfluoropropionyl chloride have been characterized using chirped pulse Fourier transform microwave spectroscopy between the frequency range of 8 and 14 GHz. Molecules were studied in separate experiments in supersonic expansions of argon. The (35)Cl, (37)Cl, and each of the monoisotopic (13)C substituted isotopologues of propionyl chloride were observed. The (35)Cl and (37)Cl isotopologues of perfluoropropionyl chloride were observed. Analyses of the resulting microwave spectra have yielded spectroscopic constants for the target molecules. The analyses indicate that, under the conditions of these experiments, both molecules are only detectable as cis conformers in which angleCCCO = 0 degrees . Comparisons are made between the electronic and geometric structure of propionyl chloride and perfluoropropionyl chloride, and also other acyl chlorides. The data produced are relevant in regards to quantifying the known destabilizing effect of perfluoroalky chains on carbonyl groups. Distinct differences in electronegativity between the CH(3)CH(2)CO- and CF(3)CF(2)CO- groups are discussed. Methyl group internal rotation is observed for propionyl chloride and has been analyzed to produce a V(3) barrier height.

The complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile determined by chirped pulse Fourier transform microwave spectroscopy.

Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8-16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed.

Pre-reactive complexes in mixtures of water vapour with halogens: characterisation of H2O...ClF and H2O...F2 by a combination of rotational spectroscopy and ab initio calculations.

Complexes H2O...ClF and H2O...F2 were detected by means of their ground-state rotational spectra in mixtures of water vapour with chlorine monofluoride and difluorine, respectively. A fast-mixing nozzle was used in conjunction with a pulsed-jet, Fourier-transform microwave spectrometer to preclude the vigorous chemical reaction that these dihalogen species undergo with water. The ground-state spectra of seven isotopomers (H2 16O...35ClF, H2 16O...ClF, H2 18O...35ClF, D2 16O... 35ClF, D2 16O...37ClF, HDO...35ClF and HDO...37ClF) of the ClF complex and five isotopomers (H2O...F2, H2 18O...F2, D2O...F2, D2 18O...Fi and HDO...F2) of the F2 complex were analysed to yield rotational constants, quartic centrifugal distortion constants and nuclear hyperfine coupling constants. These spectroscopic constants were interpreted with the aid of simple models of the complexes to give effective geometries and intermolecular stretching force constants. Isotopic substitution showed that in each complex the H2O molecule acts as the electron donor and either CIF or F2 acts as the electron acceptor, with nuclei in the order H2O...ClF or H2O...F2. For H2O...ClF, the angle phi between the bisector of the HOH angle and the O...Cl internuclear line has the value 58.9(16)degrees, while the distance r(O...Cl)= 2.6081(23) A. The corresponding quantities for H2O...F2 are phi = 48.5(21)degrees and r(O...Fi) = 2.7480(27) A, where Fi indicates the inner F atom. The potential energy V(phi) as a function of the angle phi was obtained from ab initio calculations at the aug-cc-pVDZ/MP2 level of theory for each complex by carrying out geometry optimisations at fixed values of phi in the range +/-80degrees. The global minimum corresponded to a complex of Cs symmetry with a pyramidal configuration at O in each. The function V(phi) was of the double-minimum type in each case with equilibrium values phie = +/-55.8degrees and +/-40.5degrees for H2O...ClF and H2O...F2, respectively. The barrier at the planar C2v conformation was V0= 174cm(-1) for H2O...ClF and 7cm(-1) for H2O...F2. For the latter complex, the zero-point energy level lies above the top of the barrier.

Polyps and colorectal cancer in South African Blacks.

This study reflects the fact that cancer of the large bowel is uncommon in South African Blacks, and that colorectal polyps do not appear to constitute a precursor to most colorectal cancers. Furthermore, it is shown that dietary factors associated with this cancer in Western populations are not evident in the Black population. In the South African White population, however, the disease behaves in a similar way to that observed in Western countries. Other definitive differences found were the absence of multiple synchronous cancers and diverticular disease in the Blacks with colorectal cancer. It is thus postulated that dietary factors are absent, or have not been present for a sufficient length of time to influence the development of polyps or polyp--cancer sequence in this population. It is also possible that the adenoma--carcinoma progression observed in Western countries may not be relevant to the development of all colorectal carcinomas in communities such as those reported here.

The surgical treatment of the radiation-damaged rectum.

Details are given of 37 consecutive patients with radiation damage to the rectum. Twenty-eight presented with rectovaginal fistulas, 3 with haemorrhage from ulcerative proctitis, 3 with low rectal strictures, 2 with a painful rectal ulcer and 1 with a rectal carcinoma. Thirty-five of the 37 had been treated for carcinoma of the cervix, and of these, 30 were Black South African women in whom this disease forms approximately 70 per cent of all malignancies. Associated pathology in these patients included urinary fistulas, small bowel fistulas or stenoses and a variable degree of fibrosis of the pelvic cellular tissue. Treatment involved subtotal rectal resection with restoration of continuity by means of a peranal sleeve anastomosis between healthy colon and the rectal stump denuded of its mucosa. Technical success was achieved in 35 of the 37 patients, with no mortality. The functional results were assessed both subjectively and objectively in 31 patients followed up for more than 6 months. Full continence was achieved in 54 per cent initially, improving to 75 per cent (21 of 28) at 1 year postoperatively. At 1 year, variable degrees of incontinence for a liquid stool persisted in 7 of 9 patients who had low fistulas with a low anastomosis at dentate line level. Where anastomosis was possible at a higher level, all 19 patients cured of fistula, ulcer, stenosis or haemorrhagic proctitis were fully continent at 1 year.

Transanal anastomosis in the treatment of low rectal strictures due to tribal enemas.

Enema administration is common in Black tribal communities. In the urban environment, toxic and corrosive ingredients may be used which can lead to severe complications. The diagnosis and principles of treatment of complicated proctocolitis of enema origin are discussed. The management of 2 patients who developed long stricutres extending low into the rectum is described. After subtotal rectal and sigmoid resection, continuity was successfully restored using a transanal sleeve anastomosis. Subsequent continence was normal in both patients.

Polyposis coli. The clinical spectrum in adults.

Four patients are reported, to illustrate the wide spectrum of colonic polyps which may occur in multiple form in adults. Included are unusual cases of metaplastic and juvenile polyposis. The subject is reviewed, and the need for accurate histological diagnosis is stressed. The possibility that the difference between familial adenomatous polyposis and Gardner's syndrome may lie merely in the degree of expressivity of the associated extracolonic features is discussed. Surveillance of these patients for peri-ampullary neoplasms in the duodenum is considered. The interrelationship between familial adenomatous polyposis, juvenile polyposis and colorectal cancer is discussed.

Rectal resection for tumour with transanal anastomosis and sphincter preservation.

Resection of the rectum, with restoration of continuity by means of a primary, transanal, anocolic anastomosis, is a useful method in the treatment of certain rectal tumours. It particularly fills a need in the management of tumours of the lower rectum where anterior resection is indicated but is technically difficult and liable to complications, or where it is not possible and would be abandoned in favour of abdominoperineal excision of the rectum with a permanent colostomy. The pathological criteria, technical factors and functional results which justify the use of this procedure are discussed. The principles of the operation are described, and 2 illustrative cases are reported. The large size, low site and pathological nature of both the malignant carcinoid tumour and the leiomyoma were such that total rectal resection was obligatory, the object being palliation in the former and cure in the latter. Both patients were continent after the operation. The place of this operation in the treatment of adenocarcinoma of the rectum is discussed.