The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Pure quadrupole resonance determinations of molecular charge distributions. II. Substituted pyrimidines》. Authors are Hooper, H. O.; Bray, P. J..The article about the compound:2-Amino-4,6-dichloro-5-methylpyrimidinecas:7153-13-1,SMILESS:CC1=C(N=C(N)N=C1Cl)Cl).Name: 2-Amino-4,6-dichloro-5-methylpyrimidine. Through the article, more information about this compound (cas:7153-13-1) is conveyed.
cf. C.A. 52, 7796a. The amount of double-bond character of the C-Cl bond at the 2, 4, and 6 positions was estimated from the Cl pure quadrupole resonance frequencies for the following compounds: 4-amino-6-chloro-2-methylthiopyrimidine, 6-chloro-2,4-dimethoxypyrimidine, 2,4-diamino-6-chloropyrimidine, 4,6-dichloropyrimidine, 2,4-dichloro-6-methylpyrimidine, 2,4-dichloro-5-methylpyrimidine, 2,4-dichloropyrimidine, 2,4,6-trichloropyrimidine, 2,4,5,6-tetrachloropyrimidine, 2-amino-4-chloro-6-methylpyrimidine, 2-amino-4,6-dichloro-5-methylpyrimidine, and 2-amino-5-chloropyrimidine-4-carboxylic acid. If it is assumed that the N’s have a weak inductive effect on adjacent ring positions, the calculated values for the amount of double-bond character agree well with data obtained from experiments with Zeeman splitting techniques applied to pure quadrupole resonance spectra.
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Reference:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics