STEREOCHEMISTRY OF ARSENIC: VIII. CYANODIMETHYLARSINE (CACODYL CYANIDE)

1963 ◽  
Vol 41 (2) ◽  
pp. 460-464 ◽  
Author(s):  
N. Camerman ◽  
J. Trotter
Keyword(s):  
Charge Transfer ◽  
Lone Pair ◽  
The Other ◽  
Van Der Waals Interactions ◽  
Mean Values ◽  
Bond Lengths ◽  
Nitrogen Lone Pair ◽  
The Mean ◽  
Lone Pair Electrons ◽  
Crystallographic Axes

Crystals of cyanodimethylarsine, (CH3)2AsCN, are triclinic with two molecules in a unit cell of dimensions a = 6.31, b = 8.02, c = 6.27 Å, α = 110°00′, β = 119°45′, γ = 81°47′, space group [Formula: see text]. The structure has been determined from projections along the three crystallographic axes, and the mean values of the bond lengths and valency angles (with estimated standard deviations) are: As—C = 1.96±0.03 Å, C—N = 1.16 ± 0.07 Å, [Formula: see text], [Formula: see text], [Formula: see text]. There is an unusually short As … N intermolecular separation, which is indicative of charge-transfer bonding involving donation of nitrogen lone pair electrons to vacant arsenic 4d orbitals; the other intermolecular approaches correspond to normal van der Waals interactions.

Molecular Complexes of Cyclophanes, Part XVII Charge-Transfer Complexes of [2.2]- and [2.2.2]Paracyclophane-carbamates with π-Acceptors

1987 ◽  
Vol 42 (9) ◽  
pp. 1147-1152 ◽  
Author(s):  
Aboul-fetouh E. Mourad ◽  
Verena Lehne
Keyword(s):  
Charge Transfer ◽  
Functional Group ◽  
Lone Pair ◽  
Molecular Complexes ◽  
Charge Transfer Complexes ◽  
Electronic Interactions ◽  
H Nmr ◽  
Ct Complex ◽  
Nitrogen Lone Pair ◽  
Lone Pair Electrons

Charge-transfer (CT) complexation between some [2.2]- and [2.2.2]paracyclophane-carbamates as donors with 2,3-dichloro-5.6-dicyanobenzoquinone (DDO ) as well as tetracyanoethylene (TCNE) as π-acceptors has been evidenced by VIS. 1H NMR and IR spectroscopy. The site of interaction in the two different donor systems was determined. The results reveal no contribution of the nitrogen lone pair electrons of the carbamate functional group in the CT complexation. and the interaction is mainly of π-π* type. In addition, the existence of the transannular electronic interactions in [2.2]paracyclophane derivatives is responsible for CT complex formation.

Effect of grain or silage supplementation on meat quality attributes of cryptorchid lambs grazing lucerne or annual grass-clover pastures

1995 ◽  
Vol 35 (4) ◽  
pp. 461 ◽  
Author(s):  
DL Hopkins ◽  
PJ Holst ◽  
DG Hall
Keyword(s):  
Meat Quality ◽  
Shear Force ◽  
The Other ◽  
Carcass Weight ◽  
Annual Grass ◽  
Eye Muscle ◽  
Mean Values ◽  
Significant Difference ◽  
The Mean ◽  
Ad Libitum

Objective and subjective tests for quality were performed on the meat from 40 cryptorchid second-cross lambs fed lucerne only (L; n = 8), lucerne plus an oat grain supplement ad libitum (LO; n = lo), lucerne plus wilted lucerne silage ad libitum (LS; n = 11), or an oat-lupin grain (3:1) supplement at 90% of ad libitum while grazing dry summer annual pasture (OL; n = 11). All carcasses complied with the Elite lamb specification of weight >22 kg and GR measurement 6-15 mm. There was no significant difference between groups for hot carcass weight, the mean (� s.e) values being 25.1 0.43, 25.2 � 0.36,25.2 � 0.38, and 25.3 � 0.36 kg for L, LS, LO, and OL groups, respectively. When the GR and fat depth over the eye muscle at the 12th rib were adjusted to a common carcass weight of 25.2 kg there was no significant difference between groups. There was no significant difference between groups for pH, or the colour values a*, b*, and L* of the M. longissimus thoracis et lumborum (a* is relative redness, b* relative yellowness, and L* relative lightness). The shear force values for the loin muscle were significantly (P<0.05) greater for lambs from group OL than for those from group LO. Cooking loss for the loin muscle was significantly (P<0.05) greater for OL lambs than all other groups. A comparison of the mean values for aroma and flavour showed the lambs from group OL produced meat that was considered significantly (P<0.05) less desirable for these characteristics, with other groups being similar. Meat from OL-fed lambs was considered oilier and less meaty than meat from lambs fed the other diets. There was a significant (P<0.05) difference in absolute scores between panellists, but their ranking was not affected and there was no panellist x sample interaction. Because many producers use grain supplements such as oats and lupins for finishing lambs on dry forages, further study is recommended that focuses on the interaction between supplement and the base forage.

N.M.R. spectra and stereochemistry of the bipyridyls. III. 2,2'-Bipyridyl and dimethyl derivatives, 3,3'- bipyridyl, and 4,4' - bipyridyl

1967 ◽  
Vol 20 (6) ◽  
pp. 1227 ◽  
Author(s):  
TM Spotswood ◽  
CI Tanzer
Keyword(s):  
Hydrogen Bonding ◽  
Electrostatic Field ◽  
Field Effect ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Diamagnetic Anisotropy ◽  
Equal Importance ◽  
Nitrogen Lone Pair ◽  
Lone Pair Electrons ◽  
Derivatives Of

The analysis of the n.m.r, spectra of 2,2?-, 3,3?-, and 4,4?-bipyridyl and three dimethyl-2,2?-bipyridyls is reported and the factors determining the relative chemical shifts of the ring protons and methyl groups in several solvents are discussed. The diamagnetic anisotropy of the neighbouring ring and electrostatic field effect of the nitrogen lone pair electrons are shown to be of roughly equal importance for derivatives of 2,2?-bipyridyl except in hydrogen bonding solvents. Attenuation of the electrostatic field effect in polar, and particularly in hydrogen bonding solvents, is established for 4- picoline, and for the bipyridyls, and this effect is responsible for striking changes in the spectrum of 2,2?-bipyridyl in hydrogen bonding solvents. An approximate interplanar angle of 58� is derived for 3,3?- dimethyl-2,2?-bipyridyl, and 2,2?-bipyridyl and its 4,4?- and 5,5?- dimethyl derivatives appear to be trans coplanar in all solvents. 3,3?- Bipyridyl and 4,4?-bipyridyl are probably highly twisted in all solvents, or alternatively, behave as essentially free rotors. The predicted conformations are in good agreement with the electronic spectral data.

INTRAMOLECULAR CHARGE-TRANSFER INTERACTION BETWEEN LONE PAIR ELECTRONS AND π-ELECTRON SYSTEM

1977 ◽  
Vol 6 (9) ◽  
pp. 1047-1050 ◽  
Author(s):  
Kiyoshi Mutai ◽  
Keiji Kobayashi ◽  
Tsunetoshi Kobayashi ◽  
Chikatoshi Utsunomiya
Keyword(s):  
Charge Transfer ◽  
Intramolecular Charge Transfer ◽  
Lone Pair ◽  
Electron System ◽  
Charge Transfer Interaction ◽  
Lone Pair Electrons

Elektronendichte und chemische Verschiebung der Styryldiazin- und Diazaphenanthrenprotonen / Electrondensity and Proton Chemical Shift of Styryldiazines and Diazaphenanthrenes

1972 ◽  
Vol 27 (2) ◽  
pp. 310-319
Author(s):  
H.-H. Perkampus ◽  
Th. Bluhm ◽  
J. Knop
Keyword(s):  
Ring Current ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Current Effect ◽  
Electron Densities ◽  
Paramagnetic Effect ◽  
Nitrogen Lone Pair ◽  
Chemische Verschiebung ◽  
Lone Pair Electrons ◽  
Proton Chemical Shifts

AbstractProton chemical shifts in styryldiazines and diazaphenanthrenes linearly correlate with SCF-π-electron densities of the attached carbon atom and with the electron densities of the hydrogen atom (calculated by the CNDO/2 method). The observed deviations from linearity are discussed in terms of ring current effect, steric effects and the paramagnetic effect of the nitrogen lone pair electrons. An appreciable weakening of ring current is found for diazaphenanthrenes with two adjacent N-atoms. Under the same condition the paramagnetic effect on ortho-hydrogens is increased.

Bond lengths in organic and metal-organic compounds revisited: X—H bond lengths from neutron diffraction data

2010 ◽  
Vol 66 (3) ◽  
pp. 380-386 ◽  
Author(s):  
Frank H. Allen ◽  
Ian J. Bruno
Keyword(s):  
Bond Length ◽  
Data Availability ◽  
General Level ◽  
Mean Values ◽  
Bond Lengths ◽  
Transition Metal Hydrides ◽  
Order Of Magnitude ◽  
Metal Organic ◽  
Structural Database ◽  
The Mean

The number of structures in the Cambridge Structural Database (CSD) has increased by an order of magnitude since the preparation of two major compilations of standard bond lengths in mid-1985. It is now of interest to examine whether this huge increase in data availability has implications for the mean bond-length values published in the late 1980s. Those compilations reported mean X—H bond lengths derived from rather sparse information and for rather few chemical environments. During the intervening years, the number of neutron studies has also increased, although only by a factor of around 2.25, permitting a new analysis of X—H bond-length distributions for (a) organic X = C, N, O, B, and (b) a variety of terminal and homometallic bridging transition metal hydrides. New mean values are reported here and are compared with earlier results. These new overall means are also complemented by an analysis of X—H distances at lower temperatures (T ≤ 140 K), which indicates the general level of librational effects in X—H systems. The study also extends the range of chemical environments for which statistically acceptable mean X—H bond lengths can be obtained, although values from individual structures are also collated to further extend the chemical range of this compilation. Updated default `neutron-normalization' distances for use in hydrogen-bond and deformation-density studies are also proposed for C—H, N—H and O—H, and the low-temperature analysis provides specific values for certain chemical environments and hybridization states of X.

A Simple Model for the Mean and Difference of NH-Stretching Frequencies for NH2 Groups, and Its Application to Results of Some ab initio Vibrational-Frequency Calculations

1988 ◽  
Vol 41 (3) ◽  
pp. 387
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular System ◽  
Lone Pair ◽  
Exceptional Case ◽  
Force Constants ◽  
Gauche Conformation ◽  
The Mean ◽  
The Difference ◽  
Lone Pair Electrons ◽  
The Given

The expression for the sum of the eigenvalues of the 2×2 GF matrix for two interacting NH bonds suggests that the mean NH-stretching frequency for an NH2 group should be closely proportional to ( Σf )½, where Σf is the sum of the two corresponding force constants. Ab initio results for the NH2 groups in various conformations of ethanamine , hydrazine and 1,1-dimethylhydrazine confirm such constancy to within 0.1%. The corresponding expression for the difference of the eigenvalues suggests, counterintuitively, that the difference of NH-stretching frequencies for an NH2 group in a given molecular system should also be largely proportional to ( Σf )½ and, except for the gauche conformation of 1,1-dimethylhydrazine, ab initio results for the above molecules support this suggestion to within �14 cm-1. In the exceptional case, the difference of NH-stretching force constants makes a much larger than usual contribution. Relative values of the force constants for various molecular species may be interpreted in terms of the relative geometries and effects of donation of lone-pair electrons at an adjacent centre into antibonding N-H orbitals at the given centre.

Sign in / Sign up

Export Citation Format

Share Document