Control of the orientation of the aldehyde group in 2-(alkylthio)benzaldehydes by the directional lone-pair on sulfur

1985 ◽  
Vol 63 (3) ◽  
pp. 777-781 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Kerry J. Davie ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shift ◽  
Alkyl Group ◽  
Lone Pair ◽  
Aldehyde Group ◽  
Ring Plane ◽  
Spectral Parameters ◽  
Tert Butyl ◽  
H Nmr ◽  
Lone Pairs ◽  
Repulsive Interactions

The 1H nmr spectral parameters for 2-alkylthio derivatives benzaldehyde (alkyl = CH3, CH2CH3, CH(CH3)2, C(CH3)3) are used to show that the O-syn conformation of the aldehyde group decreases from 40% for the methyl to zero for the tert-butyl compound in CC14 solution at about 300 K. It appears that the alkylthio groups twist out of the benzene plane to the same extent as in the alkyl phenyl sulfides and that it is the concomitant approaches of the 3p lone-pairs on sulfur into the ring plane which, by repulsive interactions with the C=O bond, determine the conformations of the aldehyde group. The spectral parameters display interesting changes as the size of the alkyl group increases. For example, the chemical shift of the aldehydic proton is larger than that reported for any other benzaldehyde derivative in CCl4 solution.

Das JerJ-Butyl-Kation in Lösungen von Aluminiumbromid in Mono-, Di- und Tribrommethan / The terf-Butyl-Cation in Solutions of Aluminium Bromide in Mono-, Di- and Tribromomethane

1979 ◽  
Vol 34 (7) ◽  
pp. 891-895 ◽  
Author(s):  
Peter Brüggeller ◽  
Erwin Mayer
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Dilute Solutions ◽  
Concentrated Solutions ◽  
Nmr Chemical Shift ◽  
Tert Butyl ◽  
H Nmr ◽  
Saturated Solutions

Abstract The tert-butyl cation is formed from tert-BuBr in concentrated solutions of AlBr3 in CH3Br, CH2Br2 and CHBr3 and was characterized by 1H NMR spectroscopy. Stabilization of the cation depends strongly on the AlBr3 concentration: in CH3Br saturated with AlBr3, C(CH3)3+ is formed in 80% yield; in dilute solutions of AlBr3 in CH3Br the usual de-composition occurs. In saturated solutions of AlBr3 in CH2Br2 and CHBr3 the C(CH3)3+ yield is 60 and 40%, resp. The concentration of the cation decreases in all three solvents by 20 to 30% within 10 days at room temp. In concentrated solutions of AlBr3 in CH3Br the formation of the methyl-tert-butylbromonium ion as a rapidly equilibrating species is suggested. The 1H NMR chemical shift of C(CHs)3+ in the presence of AlBr3 (δ = 5.19 in CHsBr, δ = 5.23 in CH2Br2, δ = 5.35 in CHBr3) indicates strong deshielding in comparison with shifts in SbF5 and SbF5/SO2

Spin–spin coupling between hydroxyl and aldehydic protons in some salicylaldehyde derivatives. Correlation with the hydroxyl proton chemical shift

1984 ◽  
Vol 62 (2) ◽  
pp. 326-331 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Reino Laatikainen ◽  
Salman R. Salman
Keyword(s):  
Chemical Shift ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Spectral Parameters ◽  
Hydroxyl Proton ◽  
H Nmr ◽  
Group A ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

1H nmr spectral parameters are reported for salicylaldehyde and 15 of its derivatives in dilute CCl4 solutions. In those compounds in which sufficiently large substituents are placed ortho to either of the functional groups or in which substituents enhance the charge density in the carbonyl group, a positive spin–spin coupling is observed between the two sidechain protons. This coupling, formally over five bonds, correlates with the chemical shift of the hydroxyl proton. The coupling mechanism is discussed from various viewpoints. STO 3G MO calculations give an optimized planar structure for salicylaldehyde. Nonplanar structures are less stable than the planar form. The energy of the hydrogen bond in salicylaldehyde lies near 30 kJ/mol and increases to 36 kJ/mol in the 4,6-dimethoxy derivative. Other small long-range spin–spin coupling constants in these compounds are also discussed.

119Sn, 13C and 1H NMR Spectra of Tris(1-butyl)stannyl D-Glucuronate

1997 ◽  
Vol 62 (8) ◽  
pp. 1169-1176 ◽  
Author(s):  
Antonín Lyčka ◽  
Jaroslav Holeček ◽  
David Micák
Keyword(s):  
Chemical Shift ◽  
Carbonyl Group ◽  
1H Nmr ◽  
Equatorial Plane ◽  
Title Compound ◽  
Nmr Spectra ◽  
Hydroxyl Groups ◽  
Carboxylic Group ◽  
H Nmr ◽  
Oxygen Atoms

The 119Sn, 13C and 1H NMR spectra of tris(1-butyl)stannyl D-glucuronate have been measured in hexadeuteriodimethyl sulfoxide, tetradeuteriomethanol and deuteriochloroform. The chemical shift values have been assigned unambiguously with the help of H,H-COSY, TOCSY, H,C-COSY and 1H-13C HMQC-RELAY. From the analysis of parameters of 119Sn, 13C and 1H NMR spectra of the title compound and their comparison with the corresponding spectra of tris(1-butyl)stannyl acetate and other carboxylates it follows that in solutions of non-coordinating solvents (deuteriochloroform) the title compound is present in the form of more or less isolated individual molecules with pseudotetrahedral environment around the central tin atom and with monodentately bound carboxylic group. The interaction of tin atom with oxygen atoms of carbonyl group and hydroxyl groups of the saccharide residue - if they are present at all - are very weak. In solutions in coordinating solvents (hexadeuteriodimethyl sulfoxide or tetradeuteriomethanol), the title compound forms complexes with one molecule of the solvent. Particles of these complexes have a shape of trigonal bipyramid with the 1-butyl substituents in equatorial plane and the oxygen atoms of monodentate carboxylic group and coordinating solvent in axial positions.

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.

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.

13C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

1981 ◽  
Vol 59 (20) ◽  
pp. 3007-3011 ◽  
Author(s):  
Robert R. Fraser ◽  
Noemi Chuaqui-Offermanns
Keyword(s):  
Alkyl Group ◽  
Tert Butyl

The 13C shieldings for a series of aldimines and ketimines have been measured along with the shifts for their 1-lithio derivatives. For those aldimines with a primary or secondary alkyl group attached to nitrogen, the "lithiation shifts" for the attached carbon (C-4) were all upfield due to the change from anti to syn configuration on lithiation. In the ketimines and in the N-tert-butyl aldimines and ketimines, the lithiation shifts for the C-4 carbon failed to provide stereochemical information. The shifts at C-1 and C-2 proved similar to those previously observed for lithiated alkenes.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

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.

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