Origin of alkyl substituent effect in the proton affinity of amines, alcohols, and ethers

Umeyama, Hideaki; Morokuma, Keiji

doi:10.1021/ja00431a011

Cited by 135 publications

(70 citation statements)

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“…Thus, it has been recognized that the dominant effect causing the increase of basicity with methyl substitution is the stabilization of the onium ion by the polarizability due to methyl. Probably the most satisfactory proof of that effect is given by the protonation energy decomposition method of Morokuma (18). Interestingly, the polarizability contribution in the series NH3 -+ Me3N was properly assessed only at the 4-3 1G level of calculation, STO-3G did not adequately predict this effect.…”

Section: Resultsmentioning

confidence: 99%

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

Ikuta¹,

Kebarle²

1983

Can. J. Chem.

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S. IKUTA and P. KEBARLE. Can. J. Chem. 61. 97 (1983). The proton affinities of phenyl phosphine and cyclohexylphosphinc were measured by determining the equilibrium constants of proton transfer equilibria with a pulsed electron beam high ion source pressure mass spectrometer. These proton affinities combined with values for methyl and phcnyl phosphines and the analogous amines provide an interesting comparison of the methyl and phenyl substituent effects on the basicities of phosphine and ammonia. Methyl substitution increases the basicity of both ammonia and phosphine; however, the increase is significantly larger for the phosphine. Phenyl substitution increases the basicity of ammonia and phosphine and the increase for phosphinc is very much larger. Calculations at the STO-3G, 4-3 IG, STO-3G*, and 4-31G* (* with d orbitals) for PH,, MePH,, PhPHZ, the protonated species, and the nitrogen analogues predict proton transfer reaction energies in good agreement with the experimental results. A shortening of the C-P bond is predicted for protonation of MePH, and particularly PhPH,, while a lengthening of the C-N bond is predicted for the corresponding nitrogen compounds. The much stronger increase in proton affinity of the phosphines caused by phenyl substitution is due to the stabilization of the phenyl phosphonium ion by a donation from the phenyl group to the empty orbitals of phosphorus in the PH: group; in contrast, in the amines, it is the free base anilinc which is stabilized by conjugation of the nitrogen lone pair with the aromatic ring. This stabilization of the free base is less important in phcnyl phosphine. The participating empty orbitals of phosphorus in the conjugation of phenyl with PH: in phenyl phosphonium arc mostly a * with some a d participation. The stabilization of the aniline free base contributes considerably more than the conjugation in the phosphonium ion, to the phenyl substituent difference for the amines and phosphines. Thc factors involved in the bigger substituent effect of methyl in the phosphines are somewhat similar to those for phenyl: stabilizftion of the methyl amine by conjugation of the nitrogen lone pair with empty orbitals of CH, and stabilization of the CH,PH, by hyperconjugation. An alternate description can be given in terms of hybridization chariges.S. IKUTA et P. KEBARLE. Can. J. Chem. 61, 97 (1983) On a mesure les affinitCs pour le proton de la phenylphosphine et de la cyclophosphine en determinant les constantes des Cquilibres de transfert du proton ii l'aide d'un spectromttre de masse a faisccau d'Clectrons pulses avec une source d'ions a haute pression. Ces affinitks pour le proton cornbintes aux valeurs dcs mCthyl-ct phdnyl-phosphines et des amines analogues fournissent une comparaison intkressante des effets des substituants mCthyle et phCnylc sur les basicitds de la phosphine et dc I'ammoniac. La substitution du rnCthyle augmente la basicite de la phosphine et de I'arnmoniac: I'augmentation est plus forte pour la phosphine. La substitution du phCnylc augmentc l...

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Section: Resultsmentioning

confidence: 99%

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

Ikuta¹,

Kebarle²

1983

Can. J. Chem.

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“…This is consistent with the increase in electron density on the iron center (caused by the coordinated aminoalkane group), which results in increased back-bonding to the carbonyl groups, and hence a lower m(CO) absorption frequency. A slight shift towards lower wavenumbers is observed as the carbon chain becomes longer because the nucleophilicity of aminoalkanes increases with increase in chain length [53,54].…”

Section: Reactions Of 1 With N-aminoalkanesmentioning

confidence: 99%

Synthesis and characterization of amine complexes of the cyclopentadienyliron dicarbonyl complex cation, [Cp(CO)2Fe]+

M’thiruaine

Friedrich

Changamu

et al. 2011

Inorganica Chimica Acta

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[{CpFe(CO) 2 } 2 l-(NH 2 (CH 2 ) n NH 2 )](BF 4 ) 2 (n = 2-4) (3), respectively. These complexes have been fully characterized and the mass spectral patterns of complexes 2 are reported. The structures of compounds 2a (n = 2) and 2b (n = 3) have been confirmed by single crystal X-ray crystallography. The single crystal X-ray diffraction data show that complex 2a, [CpFe(CO) 2 NH 2 (CH 2 ) 2 CH 3 ]BF 4 , crystallizes in a triclinic P 1 space group while 2b, [CpFe(CO) 2 NH 2 (CH 2 ) 3 CH 3 ]BF 4 , crystallizes in an orthorhombic Pca2 1 space group with two crystallographically independent molecular cations in the asymmetric unit. Furthermore, the reaction of 1 with 1-alkenes gives the g 2 -alkene complexes in high yield.

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“…Substitutional effects on proton affinities are well-known and substantial. [30][31][32][33][34][35][36] For a consistent set of comparisons, we computed the product structures and protonation energies of all the amines in Table 1. These computed results can be directly compared with tabulated gas-phase amine basicities, defined as the free energy of the protonation reaction, which we have taken from the NIST WebBook.…”

Section: Amine Protonationmentioning

confidence: 99%

Computational Comparison of the Reactions of Substituted Amines with CO₂

Mindrup

Schneider

2010

ChemSusChem

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Substituted amines are a popular choice as molecules to selectively react with and separate CO2 from gas mixtures. Such separations are of particular interest, for example, for CO2 separations for carbon capture and sequestration. It is desirable to tune amine–CO2 reaction energies to suit a particular separation. Herein, we use DFT‐B3LYP simulations to characterize the products and energetics of reactions of CO2 with a range of substituted amines, considering both 1:1 and 2:1 amine/CO2 reaction stoichiometries. The results show that by adjusting both the nature and the placement of functional groups, it is possible to tune reaction energies over a substantial range. Decomposition of the 2:1 reaction into separate carbamate and ammonium formation steps shows that the Brønsted basicity and Lewis basicity towards CO2 are largely uncorrelated and provide an independent means of tuning the overall reaction energies.

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Origin of alkyl substituent effect in the proton affinity of amines, alcohols, and ethers

Cited by 135 publications

References 0 publications

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

Synthesis and characterization of amine complexes of the cyclopentadienyliron dicarbonyl complex cation, [Cp(CO)2Fe]+

Computational Comparison of the Reactions of Substituted Amines with CO₂

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Origin of alkyl substituent effect in the proton affinity of amines, alcohols, and ethers

Cited by 135 publications

References 0 publications

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

Synthesis and characterization of amine complexes of the cyclopentadienyliron dicarbonyl complex cation, [Cp(CO)2Fe]+

Computational Comparison of the Reactions of Substituted Amines with CO2

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Computational Comparison of the Reactions of Substituted Amines with CO₂