The site of protonation in aniline

Pollack, Steven K.; Devlin, John L.; Summerhays, Kim D.; Taft, Robert W.; Hehre, Warren J.

doi:10.1021/ja00456a008

Cited by 72 publications

(47 citation statements)

References 1 publication

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“…b), but other competitive pathways are observed indicating ring protonation ( 1b ). Note that loss of NH 3 from 1b seems to require 1b → 1a isomerization; hence, CID‐induced isomerization may explain the contrasting results observed previously for aniline protomers sampled with different degrees of collision activation …”

Section: Resultsmentioning

confidence: 83%

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

et al. 2012

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Travelling wave ion mobility mass spectrometry (TWIM-MS) with post-TWIM and pre-TWIM collision-induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM-MS. CID performed after TWIM separation (post-TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N-protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH(3) , whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co-existing protomers of two isomeric porphyrins were also separated and characterized via post-TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO(2) loss, but a CID-resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups.

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Section: Resultsmentioning

confidence: 83%

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

et al. 2012

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“…One important benefit from the data in Table 4 is the clarification of the site of protonation that they provide. It has been shown that protonation of the nitrogen in aniline is more favorable (by -1 kcal/mol) than protonation of the ring (15,16). Without the present calculations for the phenyl phosphine it would not have been completely straightforward to decide whether ring or substituent protonation is more favorable.…”

Section: Resultsmentioning

confidence: 86%

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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“…9 Early theoretical considerations (HF/STO-3G) indicated that protonation of the amino group is only favored by 1-3 kcal/mol over the energetically most favorable ring protonation in para position. 10 As for aniline, preliminary calculations using the MP2(fc)/ 6-31G**//HF/6-31G* model lead to PAs for ammonia and the various methylamines which are some 6-7 kcal/mol higher than the experimental values. 11 Nitrogen has only one lone pair of electrons, which is relatively loosely bound and diffuse as compared to the lone pairs in oxygen or fluorine.…”

Section: Introductionmentioning

confidence: 95%

Theoretical Model Calculations of the Proton Affinities of Aminoalkanes, Aniline, and Pyridine

Hillebrand¹,

Klessinger²,

Eckert‐Maksić³

et al. 1996

J. Phys. Chem.

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It is shown that the MP2(fc)/6-311+G**//HF/6-31G*+ZPE(HF/6-31G*) theoretical model reproduces very well the experimental proton affinities (PAs) of aminoalkanes and of some of their fluoro derivatives as well as the PAs of aniline and pyridine. In all molecules considered the nitrogen is most susceptible to proton attack. PA values of amino derivatives including aniline are shown to be linearly dependent on the nitrogen lone-pair s character. Increments I(X)α are derived for the amino group and the pyridine nitrogen, which extend the set of substituent increments derived previously for an additive estimation of PA values of polysubstituted benzenes.

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The site of protonation in aniline

Cited by 72 publications

References 1 publication

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

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

Theoretical Model Calculations of the Proton Affinities of Aminoalkanes, Aniline, and Pyridine

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