Table 4.

Relative percentages of gem‐diol (GD), aldehyde (AL), hemiacetal (HA), sodium carboxylate (SC) and hydroxymethyl (ALC) forms of each pyridinecarboxaldehyde compound obtained from the ¹H‐NMR spectra under different experimental conditions.

	1H‐NMR
	A2					A3					A4
Experimental condition	GD	AL	HA	SC	ALC	GD	AL	HA	SC	ALC	GD	AL	HA	SC	ALC
0.1 M NaOH in D2O	21	48	–	21	10	70	12	–	9	9	47	43	‐	5	5
0.4 M NaOH in D2O	nd [a]					–	–	–	51	49	7	7	‐	43	43
0.1 M NaOH in CD3OD	nd [a]					–	26	74	–	–	–	4	96	–	–
0.4 M NaOH in CD3OD	nd [a]					nd [a]					–	–	81	14	5
0.1 M NaOH in DMSO‐d 6	nd [a]					–	100	–	–	–	18	82	–	–	–
0.4 M NaOH in DMSO‐d 6	nd [a]					nd [a]					40	60	–	–	–

[a] Particularly, it is very difficult to analyze this sample due to its decomposition and chemical reactions.