Stabilities of Carbonium-Ions. IV. Steric Effects in the Solvolysis of Substituted Diphenylmethyl Chlorides

1986 ◽  
Vol 39 (4) ◽  
pp. 625 ◽  
Author(s):  
R Bolton ◽  
RE Burley ◽  
NJ Williams
Keyword(s):  
Electronic Effect ◽  
Substituent Effects ◽  
Methyl Chloride ◽  
Steric Effects ◽  
Methyl Groups ◽  
Hydrogen Atoms ◽  
Carbonium Ions ◽  
Rate Of Reaction ◽  
Resonance Stabilization ◽  
Planar Transition

The replacement of ortho-hydrogen atoms by methyl groups in diphenylmethyl chloride has three distinguishable results upon the rate of solvolysis . Firstly, the alkyl groupactivates by its electronic effect; secondly, steric interactions diminish all observed substituent effects regardless of the position of the substituent in the aryl system; and thirdly, steric acceleration of the solvolysis can be seen in the rate of reaction of bis (2,6-dimethylphenyl)methyl chloride. The ortho-methyl substituents inhibit the formation of the planar transition state necessary to allow the greatest resonance stabilization by the aryl substituents of the incipient carbocation. Greater degrees of twist are reflected both in the variations in the rates of solvolysis of the poly(orthomethyl ) diphenylmethyl chlorides and in the consistent fall in the value of p+ with successive ortho-substitution.

scholarly journals Barriers to the Nucleation of Methyl Groups on the Diamond (111) Surface

1989 ◽  
Vol 155 ◽  
Author(s):  
Steven M. Valone
Keyword(s):  
Chemical Vapor Deposition ◽  
Diamond Film ◽  
Vapor Deposition ◽  
Film Growth ◽  
Chemical Vapor ◽  
Steric Effects ◽  
Methyl Groups ◽  
Hydrogen Atoms ◽  
Low Pressure Plasma ◽  
Diamond Film Growth

ABSTRACTQuestions about the mechanism of diamond film growth by low-pressure, plasma-assisted chemical vapor deposition methods have persisted for some time now. As an attempt to explore one aspect of the problem, we examine the energetics of several adsorbed diamond (111) surfaces. The adsorbates are mixtures of methyl groups and hydrogen atoms. The model for these systems is the molecular orbital hamiltonian of Dewar and coworkers.From these calculations we find that H adsorbtion is preferred due both to bond energy and steric effects. Thus, nucleation of a cluster of three or more methyl groups, as assumed in earlier work, is energetically very demanding.

Nuclear magnetic resonance characterization of the ring conformations of monosubstituted derivatives of 1,3-dioxa-5,6-benzocycloheptene

1983 ◽  
Vol 61 (1) ◽  
pp. 109-115 ◽  
Author(s):  
R. St-Amour ◽  
M. St-Jacques
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Substituent Effects ◽  
Steric Effects ◽  
Slow Exchange ◽  
Conformational Properties ◽  
Derivatives Of ◽  
Ring Conformations ◽  
Twist Boat

The conformational properties of 2-alkyl (Me, Et, i-Pr, and t-Bu) and 2-phenyl derivatives of 1,3-dioxa-5,6-benzocycloheptene (1) were studied by 13C dnmr. Analysis of slow exchange spectra at 100.6 MHz indicates that all derivatives except tert-butyl exist in an equilibrium of chair (major) and twist-boat (minor) conformations. Substituent effects on the position of the equilibrium are rationalized in terms of steric effects.

Resonance stabilization of α-ferrocenyl carbonium ions

1965 ◽  
Vol 6 (18) ◽  
pp. 1295-1302 ◽  
Author(s):  
J.C. Ware ◽  
T.G. Traylor
Keyword(s):  
Carbonium Ions ◽  
Resonance Stabilization

Electronic and steric effects on the three-fold Scholl-type cycloheptatriene ring formation around a tribenzotriquinacene core

2017 ◽  
Vol 4 (5) ◽  
pp. 817-822 ◽  
Author(s):  
Ho-Wang Ip ◽  
Hak-Fun Chow ◽  
Dietmar Kuck
Keyword(s):  
Substituent Effects ◽  
Ring Formation ◽  
Steric Effects ◽  
Electronic And Steric Effects

Single and triple bay-bridging Scholl-type cyclizations of several 1,4,8-triaryl-substituted tribenzotriquinacenes are subject to pronounced electronic and steric substituent effects.

scholarly journals Electron-induced ionization of undeuterated and deuterated benzoic acid isopropyl esters and nicotinic acid isopropyl esters: Some implications for the mechanism of the McLafferty rearrangement

2019 ◽  
Vol 26 (1) ◽  
pp. 3-24
Author(s):  
Joachim Opitz ◽  
A Stephen K Hashmi ◽  
Burkhard Miehlich ◽  
Michael Wölfle
Keyword(s):  
Benzoic Acid ◽  
Nicotinic Acid ◽  
Ethyl Ester ◽  
Methyl Groups ◽  
Aliphatic Chain ◽  
Methyl Ethyl ◽  
Hydrogen Atoms ◽  
Isopropyl Esters ◽  
Mclafferty Rearrangement ◽  
Ester Chain

Electron ionization mass spectra, ionization, and appearance energies and bond energies (as dissociation energies) are reported for benzoic acid-1-methyl-ethyl ester (BAIPE), benzoic acid-1-deutero-1-methyl-ethyl ester (BAIPED1), benzoic acid-2,2,2-trideutero-1-trideuteromethyl-ethyl ester (BAIPED6) as well as nicotinic acid-1-methyl-ethyl ester (NAIPE), nicotinic acid-1-deutero-1-methyl-ethyl ester (NAIPED1), and nicotinic acid-2,2,2-trideutero-1-trideuteromethyl-ethyl ester (NAIPED6). Ionization energies of 9.39 eV for BAIPE, 9.40 eV for BAIPED1, 9.26 eV for BAIPED6 as well as 9.70 eV for NAIPE, 9.79 eV for NAIPED1, and 9.65 eV for NAIPED6 were determined. A gas-phase formation enthalpy of [Formula: see text] = (−4.10 ± 0.1) eV for BAIPE is calculated as well as [Formula: see text] = (−3.35 ± 0.1) eV for NAIPE. Molecular ions show two main fragmentation pathways. The first is a classical McLafferty rearrangement, characterized by the transfer of one γ-hydrogen atom from the isopropyl ester chain leading to the ions of the corresponding acid and neutral propene. The second is the double hydrogen transfer from the ester chain leading to the formation of the protonated acid and a C3H5√ allyl radical. For BAIPE, both hydrogen atoms originate from the methyl groups of the aliphatic chain with a probability of ≥98%, whereas the C-1-hydrogen is transferred with a probability of ≤2%. For NAIPE, both hydrogen atoms originate from the methyl groups of the aliphatic chain with a probability of 90%. Experimental proton affinities of PA = (8.75 ± 0.2) eV for benzoic acid and PA = (8.43 ± 0.2) eV for nicotinic acid are derived. For the protonation of the carbonyl group, B3LYP DFT calculations yielded PA = 8.66 eV for benzoic acid and PA = 8.41 eV for nicotinic acid. The overall fragmentation mechanism is explained with the initial formation of a 1,5-distonic ion by transfer of the first hydrogen. For the transfer of the second hydrogen, an intermediate ion/neutral complex is formulated.

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