Lone-pair cooperativity in the N-alkylation of some derivatives of 2,2'-biimidazole

1981 ◽  
Vol 34 (12) ◽  
pp. 2569 ◽  
Author(s):  
LW Deady
Keyword(s):  
Steric Hindrance ◽  
Alkylating Agent ◽  
Alkylating Agents ◽  
Lone Pair ◽  
Lone Pairs ◽  
Close Proximity ◽  
Alkylation Reactions ◽  
Rate Ratios ◽  
Derivatives Of

The relative rates of N-alkylation of 1,1'-dimethyl-2,2'-biimidazole (6), 5,6-dihydrodiimidazo- [1,2-a:2',1'-c]pyrazine (7) and 6,7-dihydro-5H-diimidazo[l,2-a:2',1'-c][l,4]diazepine (8) with a variety of alkylating agents are reported. Irrespective of the alkylating agent, the order of reactivity was (8) (where the biimidazole has an additional three-carbon bridge) > (7) (two-carbon bridge) > (6) (no bridge), with a maximum of (8)/(6) = 317 for reaction with chloro(methoxy)methane. Since reaction of (8) is most susceptible to steric hindrance, but where the nitrogen lone pairs are in close proximity, these results support the idea of lone-pair cooperativity in the alkylation reactions. Variation in the rate ratios with changes in alkylating agent are discussed.

Through-Space Transmission of 19F-13C Coupling Via an Intermediate Bond. An Experimental and Theoretical Study

1987 ◽  
Vol 40 (12) ◽  
pp. 1923 ◽  
Author(s):  
ID Rae ◽  
ID Rae ◽  
A Staffa ◽  
A Staffa ◽  
AC Diz ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Lone Pair ◽  
Electron Excitation ◽  
Carbonyl Groups ◽  
Polarization Propagator ◽  
Close Proximity ◽  
Fermi Contact ◽  
Intramolecular Hydrogen ◽  
Intermediate Bond ◽  
Insight Into

In order to obtain a deeper insight into the title effect, several compounds with an F atom very close to a C-H of a nearby functional group were synthesized and the relevant couplings measured. The most conspicuous case was that of 8-fluoro-2-hydroxynaphthalene-1-carbaldehyde where a close proximity between the F and H atoms is the result of fluorine-oxygen repulsion and the formation of an intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The experimental four-bond J(F,CHO) coupling is 26.2 Hz. A compound very similar to this one, but without the OH group, was chosen on which to perform a polarization propagator analysis of the through-space (TS) coupling pathways, at the RPA-INDO level. The expression for the TS coupling in terms of the projected polarization propagator and perturbators was numerically analysed. It is found that this coupling is completely dominated by a TS component of the Fermi contact (FC) term, the main features of which are: ( i ) It decays exponentially with the F-H distance; (ii) Its main contribution comes from an electron excitation involving the F lone-pair, the C-H bond of the CHO moiety and its corresponding antibonding orbital;(iii) The π-type lone-pair does not contribute to the TS coupling pathway of the FC term.

The Through-Bond Interaction of a Sulfur Lone Pair with Oxygenated Substituents in the Thiacyclohexane Framework

2005 ◽  
Vol 58 (7) ◽  
pp. 531
Author(s):  
Laura Andrau ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Crystal Structures ◽  
Bond Distance ◽  
Lone Pair ◽  
X Ray ◽  
Ester Derivative ◽  
Bond Interaction ◽  
Derivatives Of ◽  
Electron Demand

Low-temperature X-ray crystal structures were determined on a range of derivatives of 4-thiacyclohexanol 5a of varying electron demand with a view to finding evidence for a through-bond interaction between the sulfur lone pair and the oxygenated substituent. In contrast to earlier suggestions, plots of C–OR bond distance versus pKa (ROH) showed that any interaction between the sulfur and the OR group is unlikely to be of a through-bond origin. Furthermore, unimolecular solvolysis rate measurements on the nosylate ester derivative 5g showed that the sulfur actually retards the reaction slightly in comparison with the corresponding sulfur-free analogue 6.

Theoretical perspective of the lone pair activity influence on band gap and SHG response of lead borates

RSC Advances ◽  
2015 ◽  
Vol 5 (97) ◽  
pp. 79882-79887 ◽  
Author(s):  
Danni Li ◽  
Qun Jing ◽  
Chen Lei ◽  
Shilie Pan ◽  
Bingbing Zhang ◽  
...  
Keyword(s):  
Band Gap ◽  
Theoretical Perspective ◽  
Lone Pair ◽  
Red Shift ◽  
Lone Pairs

Metal lone pairs play an important role in determining the SHG enhancement and bandgap red shift.

Anomalous stabilizing and destabilizing effects in some cyclic π-electron systems

1993 ◽  
Vol 71 (8) ◽  
pp. 1123-1127 ◽  
Author(s):  
Peter Politzer ◽  
M. Edward Grice ◽  
Jane S. Murray ◽  
Jorge M. Seminario
Keyword(s):  
Ab Initio ◽  
Lone Pair ◽  
Electrostatic Potentials ◽  
Electron Delocalization ◽  
Isodesmic Reaction ◽  
Computational Studies ◽  
Electron Systems ◽  
Molecular Electrostatic Potentials ◽  
Lone Pairs

Ab initio computational studies have been carried out for three molecules that are commonly classed as antiaromatic: cyclobutadiene (1), 1,3-diazacyclobutadiene (7), and 1,4-dihydropyrazine (6). Their dinitro and diamino derivatives were also investigated. Stabilizing or destabilizing energetic effects were quantified by means of the isodesmic reaction procedure at the MP2/6-31G*//HF/3-21G level, and calculated molecular electrostatic potentials (HF/STO-5G//HF/3-21G) were used as a probe of electron delocalization. Our results do not show extensive delocalization in the π systems of any one of the three parent molecules. The destabilization found for 1 and 7 is attributed primarily to strain and to repulsion between the localized π electrons in the C=C and C=N bonds, respectively. However, 6 is significantly stabilized, presumably due to limited delocalization of the nitrogen lone pairs. NH2 groups are highly stabilizing, apparently because of lone pair delocalization. NO2 is neither uniformly stabilizing nor destabilizing.

ChemInform Abstract: Highly Stereoselective Hydroxy-Alkylation, Silylation and Alkylation. Reactions of Lithium Derivatives of Chiral Phosphine Oxides.

ChemInform ◽  
2010 ◽  
Vol 28 (3) ◽  
pp. no-no
Author(s):  
C. GUEGUEN ◽  
H. J. MITCHELL ◽  
P. O'BRIEN ◽  
S. WARREN
Keyword(s):  
Phosphine Oxides ◽  
Alkylation Reactions ◽  
Derivatives Of

scholarly journals Expression and interactions of stereochemically active lone pairs and their relation to structural distortions and thermal conductivity

IUCrJ ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 480-489 ◽  
Author(s):  
Kasper Tolborg ◽  
Carlo Gatti ◽  
Bo B. Iversen
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Lone Pair ◽  
Density Functional Theory Calculations ◽  
Orbital Interaction ◽  
Void Space ◽  
Metal Compounds ◽  
Bond Angles ◽  
Lone Pairs ◽  
Bonding Effect

In chemistry, stereochemically active lone pairs are typically described as an important non-bonding effect, and recent interest has centred on understanding the derived effect of lone pair expression on physical properties such as thermal conductivity. To manipulate such properties, it is essential to understand the conditions that lead to lone pair expression and provide a quantitative chemical description of their identity to allow comparison between systems. Here, density functional theory calculations are used first to establish the presence of stereochemically active lone pairs on antimony in the archetypical chalcogenide MnSb2O4. The lone pairs are formed through a similar mechanism to those in binary post-transition metal compounds in an oxidation state of two less than their main group number [e.g. Pb(II) and Sb(III)], where the degree of orbital interaction (covalency) determines the expression of the lone pair. In MnSb2O4 the Sb lone pairs interact through a void space in the crystal structure, and their their mutual repulsion is minimized by introducing a deflection angle. This angle increases significantly with decreasing Sb—Sb distance introduced by simulating high pressure, thus showing the highly destabilizing nature of the lone pair interactions. Analysis of the chemical bonding in MnSb2O4 shows that it is dominated by polar covalent interactions with significant contributions both from charge accumulation in the bonding regions and from charge transfer. A database search of related ternary chalcogenide structures shows that, for structures with a lone pair (SbX 3 units), the degree of lone pair expression is largely determined by whether the antimony–chalcogen units are connected or not, suggesting a cooperative effect. Isolated SbX 3 units have larger X—Sb—X bond angles and therefore weaker lone pair expression than connected units. Since increased lone pair expression is equivalent to an increased orbital interaction (covalent bonding), which typically leads to increased heat conduction, this can explain the previously established correlation between larger bond angles and lower thermal conductivity. Thus, it appears that for these chalcogenides, lone pair expression and thermal conductivity may be related through the degree of covalency of the system.

Hydroxamic acids. V. The alkylation of O-alkylarylhydroxamic acids

1974 ◽  
Vol 27 (6) ◽  
pp. 1341 ◽  
Author(s):  
PM Beart ◽  
AD Ward
Keyword(s):  
Spectral Data ◽  
Alkylating Agent ◽  
Alkylating Agents ◽  
Hydroxamic Acids ◽  
Aryl Ring ◽  
Independent Synthesis ◽  
Unambiguous Assignment

The reactions of O-alkylarylhydroxamic acids with a variety of alkylating agents, to yield mixtures of the N,O-dialkyl and 0,O'-dialkyl products, are described. Spectral data and independent synthesis allow the unambiguous assignment of structure to these isomeric products. Substituents on the aryl ring exert an electronic influence on the ratio of the two products; the extent of this influence varies with the alkylating agent. Diazomethane, triethyloxonium tetrafluoroborate and methyl fluorosulphonate give largely, but not exclusively, the 0,O'-dialkyl product. Methyl fluorosulphonate, in the presence of a base, reacts further to form an unstable salt which appears also to function as an alkylating agent.

scholarly journals Endotoxin Stimulation in Patients With Lymphoma: Correlation With the Myelosuppressive Effects of Alkylating Agents

Blood ◽  
1972 ◽  
Vol 39 (5) ◽  
pp. 602-609 ◽  
Author(s):  
Ronald C. DeConti ◽  
Stephen R. Kaplan ◽  
Paul Calabresi
Keyword(s):  
Bone Marrow ◽  
Hodgkin's Disease ◽  
Alkylating Agent ◽  
Hodgkin’S Disease ◽  
Alkylating Agents ◽  
Previous Therapy ◽  
Previously Treated Patients ◽  
Previously Treated ◽  
Made In

Abstract Estimates of the bone marrow granulocyte reserve were made in 97 patients with lymphoma utilizing the endotoxin Pyrexal. Normal granulocyte responses were observed in most patients who had not received prior myelosuppressive therapy. Patients with lymphosarcoma responded as well as those with Hodgkin’s Disease. All patients with leukopenia due to previous therapy or marrow infiltration failed to respond. In the absence of leukopenia only 47% of previously treated patients achieved normal responses. The severity of granulocytopenia produced by intravenous alkylating agent therapy was correlated with pretreatment Pyrexal responses. Patients with normal granulocyte reserves, as demonstrated by this test, tolerated subsequent chemotherapy with significantly less severe granulocytopenia (p <0.02) than patients with abnormal test responses. Nadir granulocyte values below 1000 cells/cu mm developed in 7 of 33 patients with normal Pyrexal responses and in 11 of 15 abnormal responders, despite comparable pretreatment granulocyte values.

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