David W. H. Rankin

The gas-phase molecular structure of silyl(methyl)-acetylene (1-silabut-2-yne), determined by electron diffraction

Abstract The molecular structure of CH3C  CSiH3 in the gas phase has been investigated using electron diffraction. Mean amplitudes of vibration and perpendicular amplitude correction factors calculated from spectroscopic data enabled refinements of both ra and rαo structures to be carried out, allowing a comparison with the B rotation constant, corrected to Bz. Ths r0α refinement leads to a linear skeleton, with parameters: r(Si-C), 180.2(4) pm; r(CC), 121.9(4) pm; r(C-C), 145-0(5) pm; r(Si-H), 150.6(10) pm; r(C-H), 105.3(7) pm; ∠-HSiC, 110.7(10)°; ∠HCC, 110.9(12)°. The ra structure shows the usual apparent bends in the skeleton due to shrinkage.

The molecular structure of difluorophosphine selenide,determined using a combination of gas electron diffraction and liquid-crystal NMR data

Abstract The molecular structure of difluorophosphine selenide has been determined by a combined analysis of gas-phase electron diffraction data and dipolar couplings obtained for a solution in a nematic phase. Geometrical parameters ( r a ) are: r (PSe) 202.6(4), r (P-F) 155.7(3), r (P-H) 142.2(7) pm, ∠SePF 116.8(3), ∠FPF 98.1(7), ∠SePH 118.6(7)°.

Electron diffraction determination of the molecular structures of methylazide, methylisocyanate and methylisothiocyanate in the gas phase

Abstract The structures of methylisocyanate, methylisothiocyanate, and methylazide in the gas phase have been determined by electron diffraction. The principal bond lengths and angles for CH3NCO are r(C-N) = 145.0 ± 0.4 pm, r(NC) = 116.8±0.5 pm, r(CO) = 120.2±0.5 pm, ∠CNC = 2.448± 0.007 rad; for CH3NCS, r(C-N) = 147.9 ± 0.8 pm, r(NC) = 119.2 ± 0.6 pm, r(CS) = 159.7 ± 0.5 pm, ∠CNC = 2.471 ± 0.007 rad; for CH3N3, r(C-N) = 146.8 ± 0.5 pm, r(NN) = 121.6 ± 0.4pm, r(NN) = 113.0 ± 0.5pm, ∠CNN = 2.038 ± 0.005 rad.

An electron diffraction determination of the molecular structure of methyl silyl ether

Abstract The molecular structure of methyl silyl ether CH 3 OSiH 3 , has been deter- mined in the gas phase by the sector microphotometer method of electron, diffrac- tion. The Si-O bond length is 1.640±0.003 A, the C-O bond length is 1.418±0.009 A, and the Si-O-C angle is 120.6±0.9°.

Structured Type 1 Diabetes Education Delivered Within Routine Care Impact on glycemic control and diabetes-specific quality of life

OBJECTIVE To determine whether improvements in glycemic control and diabetes-specific quality of life (QoL) scores reported in research studies for the type 1 diabetes structured education program Dose Adjustment For Normal Eating (DAFNE) are also found when the intervention is delivered within routine U.K. health care. RESEARCH DESIGN AND METHODS Before and after evaluation of DAFNE to assess impact on glycemic control and QoL among 262 adults with type 1 diabetes. RESULTS There were significant improvements in HbA1c from baseline to 6 and 12 months (from 9.1 to 8.6 and 8.8%, respectively) in a subgroup with suboptimal control. QoL was significantly improved by 3 months and maintained at both follow-up points. CONCLUSIONS Longer-term improved glycemic control and QoL is achievable among adults with type 1 diabetes through delivery of structured education in routine care, albeit with smaller effect sizes than reported in trials.

The molecular structure of tetra-tert-butyldiphosphine: an extremely distorted, sterically crowded molecule

The molecular structure of tetra-tert-butyldiphosphine has been determined in the gas phase by electron diffraction using the new DYNAMITE method and in the crystalline phase by X-ray diffraction. Ab initio methods were employed to gain a greater understanding of the structural preferences of this molecule in the gas phase, and to determine the intrinsic P-P bond energy, using recently described methods. Although the P-P bond is relatively long [GED 226.4(8) pm; X-ray 223.4(1) pm] and the dissociation energy is computed to be correspondingly small (150.6 kJ mol(-1)), the intrinsic energy of this bond (258.2 kJ mol(-1)) is normal for a diphosphine. The gaseous data were refined using the new Edinburgh structure refinement program ed@ed, which is described in detail. The molecular structure of gaseous P(2)Bu(t)(4) is compared to that of the isoelectronic 1,1,2,2-tetra-tert-butyldisilane. The molecules adopt a conformation with C(2) symmetry. The P-P-C angles returned from the gas electron diffraction refinement are 118.8(6) and 98.9(6) degrees, a difference of 20 degrees, whilst the C-P-C angle is 110.3(8) degrees. The corresponding parameters in the crystal are 120.9(1), 99.5(1) and 109.5(1) degrees. There are also large deformations within the tert-butyl groups, making the DYNAMITE analysis for this molecule extremely important.

Structures and Aggregation of the Methylamine−Borane Molecules, MenH3−nN·BH3 (n = 1−3), Studied by X-ray Diffraction, Gas-Phase Electron Diffraction, and Quantum Chemical Calculations

The structures of the molecules methylamine-borane, MeH(2)N.BH(3), and dimethylamine-borane, Me(2)HN.BH(3), have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations. The crystal structures have also been determined for methylamine-, dimethylamine-, and trimethylamine-borane, Me(n)H(3-n)N.BH(3) (n = 1-3); these are noteworthy for what they reveal about the intermolecular interactions and, particularly, the N-H...H-B dihydrogen bonding in the cases where n = 1 or 2. Hence, structures are now known for all the members of the ammonia- and amine-borane series Me(n)H(3-n)N.BH(3) (n = 0-3) in both the gas and solid phases. The structural variations and energetics of formation of the gaseous adducts are discussed in relation to the basicity of the Me(n)H(3-n)N fragment. The relative importance of secondary interactions in the solid adducts with n = 0-3 has been assessed by the semi-classical density sums (SCDS-PIXEL) approach.

The molecular structure of n-methyldisilylamine

Abstract The molecular structure of N-methyldisilylamine, (SiH 3 ) 2 NCH 3 , in the gas phase has been determined by the sector microphotometer method of electron diffraction. The heavy atoms are coplanar, with a Si-N-Si angle of 125.4 ± 0.4°: the Si-N and C-N bond lengths are 1.726 ± 0.003 A and 1.465 ± 0.005 A respectively. These results are compared with those for disilylamine.

The molecular structure of monomeric n-silyldimethylamine

Abstract The molecular structure of monomeric N-silyldimethylamine, SiH 3 N(CH 3 ) 2 , has been determined in the vapour phase by the sector-microphotometer method of electron diffraction. The Si-N and C-N bond lengths are 1.715 ± 0.004 A and 1.462 ± 0.004 A, respectively: the Si-N-C and C-N-C angles are 120.0 ± 0.4° and 111.1 ± 1.2°, respectively.

The molecular structure of pyridine in the gas phase determined from electron diffraction, microwave and infrared data and ab-initio force-field calculations

Abstract The gas-phase molecular structure of pyridine was studied by joint analysis of electron diffraction, microwave and infrared data, augmented by vibrational constraints taken from force-field calculations at the 4-21G ab-initio level. Geometrical constraints arising from 4-21G, 4-31G, 4-21GN* and microwave results were tested. The 4-21GN* constraints were significantly better than the others. The range of models that fit all available experimental data was then investigated with respect to the difference between the CNC and NCC valence angles. This resulted in the following best-fitting model ( r g distances, r 0 α angles): NC = 1.344 A; C 2 C 3 = 1.399 A; C 3 C 4 = 1.398 A; CH (average) = 1.094 A; CNC = 116.1°; NCC = 124.6°; C 2 C 3 C 4 = 117.8°; C 3 C 4 C 5 = 119.1°; NCH = 115.2°. The data suggest that the perturbation resulting from the N atom is primarily in the CNC part of the ring.