Textbook Error, 138: Bhinyo Panijpan Department of Biochemistry Faculty of Science Mahidoi University Bangkok 4. Thailand
The Singly Protonated Structure of Thiamine
I
Basicity of the heterocyclic nitrogen versus NH2 nitrogen
The monopmtonated form of thiamine as illustrated in many undergraduate textbooks and authoritative works has the most acidic hydrogen atom associated with the pyrimidine
A pyrimidine derivative used to couple with the thiazole moiety in the classical synthesis ( I ) of thiamine is usually represented as IIa or IIb. These representations explicitly show the protonation of the amino group (Ia and IIa) or implicitly indicate preferred interaction between the extracyclic nitrogen and H of the hydrogen halide (Ib and Ilb).
However, spectroscopic studies on solutions and X-ray diffraction work on crvstals of such 4-amino~vrimidines. .. thiamine-: and deri\,at~vt.sI C H US ~ to the definiteconclusion that the N
