Bond contraction and lone pair interaction at nitride surfaces

2001 ◽  
Vol 90 (5) ◽  
pp. 2615-2617 ◽  
Author(s):  
C. Q. Sun ◽  
B. K. Tay ◽  
S. P. Lau ◽  
X. W. Sun ◽  
X. T. Zeng ◽  
...  
Keyword(s):  
Lone Pair ◽  
Pair Interaction

1H and 13C nuclear magnetic resonance studies of the conformational equilibrium of 2-(diphenylphosphino)benzaldehyde in polar and nonpolar solutions. Signs of the proximate coupling constants, 4J(CHO, 31P) and 3(13CHO, 31P)

1993 ◽  
Vol 71 (9) ◽  
pp. 1384-1393 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Robert W. Schurko ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Lone Pair ◽  
Pair Interaction ◽  
Coupling Constants ◽  
Torsion Angles ◽  
Solvent Dependence ◽  
13C Nuclear Magnetic Resonance ◽  
Repulsive Forces ◽  
Nuclear Magnetic

The analyses of the 1H nuclear magnetic resonance spectra of 2-(diphenylphosphino)benzaldehyde in CS2/C6D12 and acetone-d6 solutions yield stereospecific coupling constants from which the populations of the O-cis and O-trans conformers are derived. The free energy differences favouring the O-trans conformer at 300 K are 2.7 and 0.9 kJ/mol, in the polar and nonpolar solutions, respectively; in the crystal only the O-cis conformer exists. The coupling constant, 4J(CHO, P), is estimated as −7.1(2) Hz in the O-trans confomer and 3J(CHO, P) as +29.4(1.3) Hz. Their magnitudes depend on the proximity of the C—H bond to the lone pair on phosphorus. nJ(C, P) are reported for triphenylphosphine and for the benzaldehyde derivative as dilute solutions in the two solvents, demonstrating a significant solvent dependence for some of these coupling constants. Some simple relationships are proposed between nJ(C, P) and the torsion angle about the C—P bond, estimates of the latter coming from AM1 and STO 3G MO computations. nJ(C, P) are also sensitive to intrinsic ring substituent perturbations, as are the nJ(H, P); for example, 5J(H, P) is negative in the disubstituted ring of 2-(diphenylphosphino)benzaldehyde but positive in the phenyl groups. The nJ(H, P) are also discussed with respect to their dependence on the torsion angles about the C—P bonds. It appears that the conformational properties of the aromatic rings in triphenylphosphine and its formyl derivative are very similar. Further, the phosphorus atom is polarized such that the carbonyl bond is attracted towards the positive region near phosphorus, and the C—H bond of the formyl group more towards the lone-pair region; the actual torsion angles represent a compromise between these attractive forces and the repulsive forces between bonds on neighbouring aromatic moieties. CNDO/2 MO and INDO MO FPT computations of nJ(C, P) and nJ(H, P) are of mixed utility, although the former bear out the idea that the proximate [Formula: see text]lone-pair interaction dominates 3J(CHO,P) and 4J(CHO,P).

scholarly journals The effect of nitrogen lone-pair interaction on the conduction in a single-molecule junction with amine-Au bonding

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
Yoshihiro Sugita ◽  
Atsushi Taninaka ◽  
Shoji Yoshida ◽  
Osamu Takeuchi ◽  
Hidemi Shigekawa
Keyword(s):  
Single Molecule ◽  
Lone Pair ◽  
Pair Interaction ◽  
Molecule Junction ◽  
Nitrogen Lone Pair ◽  
Single Molecule Junction

Protonation and Acid-catalyzed Rearrangement of 1,2-Diazepines

1974 ◽  
Vol 52 (15) ◽  
pp. 2805-2817 ◽  
Author(s):  
David John Harris ◽  
M. T. Thomas ◽  
Victor Snieckus ◽  
E. Klingsberg
Keyword(s):  
Activation Energy ◽  
Trifluoroacetic Acid ◽  
Water Solution ◽  
Spectral Characteristics ◽  
Lone Pair ◽  
Pair Interaction ◽  
Protonated Form ◽  
Open Chain ◽  
Ring Inversion ◽  
The Difference

The protonation of the 1,2(4H)-diazepines 2a, 2b, and the 1,2(1H)-diazepine 3a in various acidic media has been studied by u.v. and n.m.r. spectroscopy. Compounds 2a and 3a undergo protonation to give 4a and 7a, respectively, whereas 2b provides the monoprotonated species 4b in dilute acid and the diprotonated form 4c in strongly acidic solution. Spectral characteristics of crystalline 1,2(4H)-diazepinium perchlorates 4a, 4d, 7a, and 7c correlate well with those observed for the corresponding free bases in acidic solutions; 7a-ClO4 and 7c-ClO4 were obtained either from 2a and 2c or from 3a and 3c, respectively. In trifluoroacetic acid-d-D2O, deuterium exchange at C4 and C6 of 2a, 2b, and 3a was observed indicating the presence of small equilibrium concentrations of species 1a, 1c and/or 1d, and 1b under these conditions. Temperature variable n.m.r. spectroscopy provides evidence for ring inversion phenomena for the protonated forms 4a and 7a. In the case of 4a, the activation energy, ΔGc≠ = 10.2 ± 0.2 kcal/mol (Tc = 8 ± 3°) has been estimated. The difference in the activation energy between the free base and the protonated form, ΔG≠ (2a)—ΔG≠ (4a) = 6–7 kcal/mol is attributed to strong repulsive N1—N2 lone pair interaction in 2a in the transition state for the ring inversion process.Under vigorous acidic conditions, the 1, 2(4H)-diazepines 2a–c give pyrazoles (10a–c), pyridines (12a–c), and acetophenone. Using identical conditions, the 1,2(4H)-diazepinium salt, 7a-ClO4 provides pyrazole 11a and pyridine 12a and, in addition, the 1-methylaminopyridinium salt 13a. However, rearrangement also proceeds under very mild conditions (ethanol–water) as shown for 7a-ClO4 and 7c-ClO4 which yield compounds 11a and 12a, and 11c, 12c, and 13c, respectively. The 1, 2(1H)-diazepine 3a gives 11a, 12a, and 13a in ethanol–water solution and exclusively 13a in trifluoroacetic acid. The mechanism of these reactions is discussed in terms of formation of open-chain (15) and diaziridine-type (19) intermediates. Electrocylic mechanisms are eliminated from consideration on the basis of the absence of products 23, 24, and 25 which should have been observed from the reactions of 2b, 2c, and 7c-ClO4 if these pathways were operative.

Molecular force field for chlorine trifluoride

1965 ◽  
Vol 18 (3) ◽  
pp. 261 ◽  
Author(s):  
MG Krishna ◽  
K Ramaswamy ◽  
R Pichai
Keyword(s):  
Force Field ◽  
Force Constant ◽  
Lone Pair ◽  
Pair Interaction ◽  
Pair Bond ◽  
Approximate Relation ◽  
Lone Pairs ◽  
Bond Pair ◽  
Molecular Force ◽  
Molecular Force Field

An attempt has been made to modify the UBFF for chlorine trifluoride by taking into account the presence of lone pairs of electrons, on the lines suggested by Pariseau, Wu, and Overend. It was found that the lone-pair-bond-pair interaction is less than the lone-pair-lone-pair interaction which is considerably lower than the stretching force constant for the lone pair of electrons. An approximate relation between the above interactions was obtained.

N,N-dimethyl-p-anisidinium cation. Esr evidence for intermolecular spin-lone pair interaction

1985 ◽  
Vol 26 (51) ◽  
pp. 6369-6372 ◽  
Author(s):  
F. Ciminale ◽  
R. Curci ◽  
L. Troisi
Keyword(s):  
Lone Pair ◽  
Pair Interaction

Asymmetric Total Syntheses of (+)-3-(Z)-Laureatin and (+)-3-(Z)-Isolaureatin by “Lone Pair−Lone Pair Interaction-Controlled” Isomerization

2007 ◽  
Vol 129 (8) ◽  
pp. 2269-2274 ◽  
Author(s):  
Hyoungsu Kim ◽  
Hyunjoo Lee ◽  
Dongjoo Lee ◽  
Sanghee Kim ◽  
Deukjoon Kim
Keyword(s):  
Lone Pair ◽  
Pair Interaction ◽  
Total Syntheses

Structural Information from the Integrated Intensity of the OH-Stretching Band of Saturated Alcohols

1986 ◽  
Vol 40 (8) ◽  
pp. 1093-1098 ◽  
Author(s):  
F. A. J. Singelenberg ◽  
E. T. G. Lutz ◽  
J. H. Van Der Maas
Keyword(s):  
Structural Information ◽  
Lone Pair ◽  
Pair Interaction ◽  
Primary Alcohols ◽  
Intensity Factors ◽  
Methyl Group ◽  
Tertiary Alcohols ◽  
A Value ◽  
Integrated Intensity ◽  
Oxygen Lone Pair

The integrated intensity, A, of the free OH-stretching band of a large number of noncyclic and six-membered cyclic saturated monohydroxy compounds has been studied as a possible source of structural information. The intensity of primary alcohols proves to be constant, viz., 16.8 ± 0.5 km/M. No factors have been found that influence this value. The standard A-value for secondary alcohols is 13.8 ± 0.4 km/M. OH-rotamers without trans-H-Oxygen-lone-pair interaction show a lower intensity; factors influencing the rotamer distribution might thus affect the overall A-value. A significant decrease is observed when a γ-methyl group is situated (very) close to and therefore strongly interacts with a lone pair of the oxygen atom. The standard A-value for tertiary alcohols is 11.2 ± 0.6 km/M. Initially all rotamers have the same A-value, but for the secondary ones a strongly interacting γ-methyl group may cause an appreciable intensity lowering. Besides, strong sterical interactions between the three alkyl substituents at the α-C-atom usually give rise to small changes in the intensity. The overall conclusion is that the integrated intensity proves to be a useful source of structural information.

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