Concerning the Ortho Shift in Proton and Fluorine Magnetic Resonance of Some Conjugated Hydrocarbons

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An additivity scheme which takes into account the interactions between ortho substituents is applied to 39 proton shifts in 22 tri-, tetra-, and pentasubstitutcd halobenzenes as 3 mole % solutions in cyclohexane and carbon tetrachloride. The shift of any proton can be written as the sum of two parameters D ( X , Y ) and one parameter d,. D ( X , Y ) refers to a pair of substituents placed ortho ( X ) and meta ( Y )to the proton and d, refers to a substituent placed para to the proton. The mean deviation between observed and calculated shifts is found to be 0.010 p.p.m. for the cyclohexane solutions and 0.012 p.p.m. for the carbon tetrachloride solutions. The scheme also works reasonably well for mono and dihalobenzenes. The parameteris a measure of the stcric interaction between the X and Y substituents. It is also suggested that the steric environment of a proton is important in determining the shift in carbon tetrachloride solution.

Section: Introductionmentioning

confidence: 99%

Proton chemical shifts of polyhalobenzenes in cyclohexane and carbon tetrachloride. An additivity scheme based on pairwise parameters

Richardson¹,

Schaefer²

1968

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“…The methyl proton shifts of propene and the halopropenes are given in Table 11. 6The Q correlation also works well for fluorine shifts (1). In addition to ortho fluorine shifts in Although not all the shifts are in ortho-substituted monofluorobenzenes and in penta-TRlS solvent, where medium effects are fluorophenyl compounds, it applies to, for example, the ortho shifts in 2-X perAuorobiphenyls (11) s and Lmns proton shifts in the vinyl and propene than Such differences not subseries had not been noted previously.…”

Section: Predicted Observed In Tms Ch3mentioning

confidence: 76%

Solvent effects on the proton spectra of some halopropenes. The preparation and proton resonance spectra of the 1-iodopropenes

Hruska¹,

McBride²,

Schaefer³

1967

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The preparation and proton resonance spectra of the 1-iodopropenes are reported and solvent effects on the proton spectra of the chloro-, bromo-, and iodo-compounds are measured. The proton coupling constants are discussed in terms of old and new electronegativity correlations. The olefinic cis and trans proton shifts can be attributed mainly to a paramagnetic contribution from the substituent, whereas the gem olefinic proton shifts depend in addition on the electron-withdrawing power of the substituent. The methyl proton shifts in the l-substituted compound show little dependence on the substituent and this is discussed in relation to the barrier heights to methyl rotation. The solvent shifts in benzene cannot be completely reconciled with a dipole -induced dipole model. They increase with the size of the substituent and are largest for protons farthest from the substituent. The solvent shifts in acetone can be explained as due to weak hydrogen bonding and reaction field effects. The shifts of protons genz to the substituent arise mainly from hydrogen bonding, whereas the shifts of protons cis or trans have significant contributions from both effects. The reaction field effects can also account for the methyl shifts in acetone.

“…Thus it is entirely possible that the predicted P is not a pure factor but rather some linear combination of the actual ortho factor and u l and/or u:. As an alternative, we also tried Schaefer's semi-empirical Q parameter (27), as modified by Smith for use as a predictor of ortho "C chemical shifts (28). There is fairly good agreement between input and predicted Q (see Table 7).…”

Section: (0 Factor Analysis Incorporating Short-rcznge Chemical Shiftsmentioning

confidence: 99%

Substituent-induced chemical shifts in 3- and 4-substituted styrenes: factor analysis of the styrene data matrix

Reynolds¹,

Gomes²,

Maron³

et al. 1983

The techniques of factor analysis are used to investigate a data matrix constructed from magnetic resonance parameters for seventy-five 4-substituted styrenes, α-methylstyrenes, and α-tert-butylstyrenes and 3-substituted styrenes and α-methylstyrenes (with fifteen common substituents for each series). Two substituent factors (parameters) are clearly both necessary and sufficient to predict long-range chemical shifts within experimental uncertainty. Target testing indicates that Taft's σ1 and [Formula: see text] constants are appropriate for this purpose. One additional major factor is required for each of ipso and ortho carbons and a minor factor is apparently required for meta carbons.Conclusions do not appear to be sensitive to the weighting of individual variables and the specific variables included in the data matrix. However, the use of an extensive and well-chosen substituent set is essential.