1. (a) Shaik SS, Schlegel HB, Wolfe S (1992) Theoretical aspects of physical organic chemistry: the SN2 mechanism. Wiley, New York. See particularly Introduction and chapters 1 and 2; (b) Marcus RA (1990) Science 256:1523; (c) For a very abstract and mathematical but interesting treatment, see Mezey PG (1987) Potential energy hypersurfaces. Elsevier, New York; (d) Steinfeld JI, Francisco JS, Hase WL (1999) Chemical kinetics and dynamics, 2nd edn, Prentice Hall, Upper Saddle River
2. Levine IN (2014) Quantum chemistry, 7th edn. Prentice Hall, Upper Saddle River, section 4.3
3. Reference [1a], pp 50–51
4. (a) Houk KN, Li Y, Evanseck JD (1992) Angew Chem Int Ed Engl 31:682; (b) Leach AR (2001) Molecular modeling. Principles and applications. Prentice Hall, Upper Saddle River, p 281
5. Atkins P (1998) Physical chemistry, 6th edn. Freeman, New York, pp 830–844