1. Ottaway JM. In: Bishop E, editor. Indicators. Pergamon Press, 1972 [chapter 8A].
2. Reichardt C. Solvents and solvent effects in organic chemistry. Weinheim: VCH, 1990 [chapter 6].
3. Bruylants A, Feytmant-De Medecis E. In: Patai S, editor. The chemistry of the carbon-nitrogen double bond, John Wiley & Sons, 1970 [chapter 10].
4. March J. Advanced organic chemistry. New York: John Wiley & Sons, 1992. p. 884–5, and references therein.