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Ortho Substituents (ortho + substituent)
Selected AbstractsChemInform Abstract: Expeditious Synthesis of Benzopyrans via Lewis Acid-Catalyzed C,H Functionalization: Remarkable Enhancement of Reactivity by an ortho Substituent.CHEMINFORM, Issue 34 2010Keiji Mori Abstract ortho-Substitution to the alkoxy group enhances the reactivity of the substrates and leads to the higher yields of the corresponding products [cf. [source] Remarkably Slow Rotation about a Single Bond between an sp3 -Hybridised Carbon Atom and an Aromatic Ring without ortho SubstituentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2009Sarah Murrison Abstract Look, noorthosubstituents! A series of polycycles were prepared by using a three-component Joullié,Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured, and was highly dependent on the substitution. Rotamer half-lives of up to 21,h at 298,K were observed (see figure). Rotamers resulting from this restricted rotation were isolated for the first time. A series of polycycles was prepared by using a three-component Joullié,Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured by using, in general, variable-temperature HPLC. The rate of rotation was highly dependent on substitution and rotamer half-lives of up to 21,h at 298,K were observed. Insights into the effect of substitution on the rate of rotation were gleaned through electronic structure calculations on closely related derivatives. Rotamers resulting from restricted rotation about a bond between an sp3 -hybridised carbon atom and a phenyl ring with no ortho substituents were isolated for the first time, and the equilibration of the separated rotamers was followed by using analytical HPLC. It was demonstrated, for the first time, that a highly hindered environment for the sp3 -hybridised atom is sufficient for slow bond rotation about a single bond between sp3 - and sp2 -hybridised carbon atoms. [source] Computational Study of the Lipase-Mediated Desymmetrisation of 2-Substituted-Propane-1,3-DiaminesCHEMBIOCHEM, Issue 18 2009Eduardo García-Urdiales Dr. Abstract The enantioselectivity displayed by the lipase from Pseudomonas cepacia towards a wide range of prochiral 2-substituted-propane-1,3-diamines was studied by means of molecular dynamics simulations (MDS). In all cases the enzyme allows the recovery of the corresponding amino carbamates of R configuration. However, the enantioselectivity is only synthetically useful if no ortho substituent is present and the aromatic ring is directly bonded to the 2-carbon of the 1,3-diamine core. Analysis of the MDS trajectories revealed that the homologation of 2-aryl substituents by means of a methylene group lowers enantioselectivity by alleviating the conformational tension of the slow-reacting orientations due to unfavourable intramolecular contacts between the ortho carbons of the aryl group and the nucleophilic nitrogen, as well as between the chiral carbon and the oxyanion. Additionally, the relative solvent accessible surfaces of the atoms of the aryl ring nicely correlate with the effect of the location of the substituent on enantioselectivity. [source] X-ray Crystal Structure Study of Sterically Congested DiphenyldiazomethanesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2004Takashi Iikubo Abstract X-ray crystallographic structures were determined for five diphenyldiazomethanes (DDMs) with various ortho substituents, namely, bis(2,4,6-trichlorophenyl)diazomethane, bis(2,4,6-tribromophenyl)diazomethane, bis(4- tert -butyl-2,6-dibromophenyl)diazomethane, (4- tert -butyl-2,6-dimethylphenyl)(2,4,6-tribromophenyl)diazomethane, and [4- tert -butyl-2,6-bis(trifluoromethyl)phenyl](4- tert -butyl-2,6-dibromophenyl)diazomethane, and for bis(4-bromophenyl)diazomethane, a DDM with no ortho substituents. The correlation between the structural parameters, the ESR zero-field splitting (ZFS) parameters and the lifetimes of the triplet diphenylcarbenes (DPCs) generated from these diazo compounds was examined. It is noted that as ortho substituents are introduced onto the phenyl rings of the DDMs, the interplanar angle between the two phenyl rings increases, while the angle of the diazo carbon changes very little. DDM 6 -N2, from which the longest-lived triplet carbene is generated, is shown to have the largest interplanar angle of the DDMs examined. The bond distances between the aromatic carbons and the ortho substituents as well as the van der Waals radii of the substituents were also examined. These studies do not provide a quantitative correlation between the structural parameters of the precursor DDMs and the ZFS parameters and lifetimes of their photoproducts, triplet DPCs, but show how steric shielding of the ortho substituents affects the structures and stabilities of triplet DPCs. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acidJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2006Vilve Nummert Abstract Infrared spectra of 25 substituted phenyl esters of benzoic acid C6H5CO2C6H4 -X (XH, 3-Cl, 3-F, 3-CN, 3-NO2, 3-CH3, 3-OH, 3-NH2, 4-Cl, 4-F, 4-NO2, 4-CN, 4-OCH3, 4-CH3, 4-NH2, 2-Cl, 2-F, 2-I, 2-NO2, 2-CF3, 2-CN, 2-CH3, 2-OCH3, 2-N(CH3)2, 2-C(CH3)3), 8 alkyl benzoates C6H5CO2R (XCH3, CH2CH3, CH2Cl, CH2CN, CH2CCH, CH2CH2Cl, CH2CH2OCH3, CH2C6H5), and 22 phenyl esters of substituted benzoic acids X-C6H4CO2C6H5 (X3-Cl, 3-NO2, 3-CH3, 3-N(CH3)2, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-C(CH3)3, 4-OCH3, 4-NH2, 2-Cl, 2-F, 2-Br, 2-I, 2-NO2, 2-CN, 2-CF3, 2-CH3, 2-OCH3, 2-NH2) were recorded in tetrachloromethane in the region of 400,4000,cm,1. Carbonyl stretching frequencies ,CO for meta - and para -substituted phenyl esters of benzoic acid and phenyl esters of meta -substituted benzoic acids were shown to correlate with the substituent constants ,o. The influence of the through resonance effect on ,CO was found to be important in the case of +Rpara substituents in the benzoyl part of phenyl benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate with the inductive substituent constant ,I only. In the benzoyl part of the esters the carbonyl stretching frequencies of cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter equations: (,CO)cis,=,(,CO)o,+,c1,I,+,c3,and (,CO)trans,=,(,CO)o,+,c1,p+,+,c3, (R,=,0.99). The trans isomers of phenyl esters of ortho -substituted benzoic acids showed direct resonance similar to that for para derivatives. The positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition of resonance between the phenyl ring and the carboxy-group caused by bulky ortho substituents. The existence of cis/trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at B3LYP/6-311+G** level for the ortho -substituted benzoates. In the case of alkyl benzoates good correlations of ,CO values were obtained when both the Taft ,* and the steric constants were used. For meta - and para -substituted phenyl benzoates s - trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular relative to the carbonyl bond plane was supported. Copyright © 2006 John Wiley & Sons, Ltd. [source] Remarkably Slow Rotation about a Single Bond between an sp3 -Hybridised Carbon Atom and an Aromatic Ring without ortho SubstituentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2009Sarah Murrison Abstract Look, noorthosubstituents! A series of polycycles were prepared by using a three-component Joullié,Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured, and was highly dependent on the substitution. Rotamer half-lives of up to 21,h at 298,K were observed (see figure). Rotamers resulting from this restricted rotation were isolated for the first time. A series of polycycles was prepared by using a three-component Joullié,Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured by using, in general, variable-temperature HPLC. The rate of rotation was highly dependent on substitution and rotamer half-lives of up to 21,h at 298,K were observed. Insights into the effect of substitution on the rate of rotation were gleaned through electronic structure calculations on closely related derivatives. Rotamers resulting from restricted rotation about a bond between an sp3 -hybridised carbon atom and a phenyl ring with no ortho substituents were isolated for the first time, and the equilibration of the separated rotamers was followed by using analytical HPLC. It was demonstrated, for the first time, that a highly hindered environment for the sp3 -hybridised atom is sufficient for slow bond rotation about a single bond between sp3 - and sp2 -hybridised carbon atoms. [source] | ||||||||||