Mechanism of the esterification of boric acid with aliphatic diols

Calculations at the  B3LYP+GD3+BJ/Def2-TZVPP/SCRF=CPCM/Water level at DOI: 10.14469/hpc/14410

Ammonium cation					  -57.012455
Tetrahydroxyborate anion		 -328.600539 
		Ion-separated   	   = -385.612994
		Intimate			   = -385.628483
Boric acid						 -252.607946
Pentanediol						 -348.255435
 
Reactant as separated ions 		=-986.476375							
Reactant as supermolecule  		=-986.483328, -4.36 kcal/mol lower. (-986.489411 TZVPPD) [-986.545247 QZ] {-985.712909. B2PLYPD3}

TS2 as  supermolecule:			 -986.468508
TS3 as  supermolecule            -986.473456  ΔG 6.2 kcal/mol, 26.0 kJ (-986.478748 TZVPPD, ΔG 6.7)[-986.534018 QZ, ΔG 7.0] {-985.703297, B2PLYPD3, ΔG 6.0}
TS3 as  separated ions:			 -986.461683  (-929.449228 + -57.012455; +7.4 kcal/mol vs SM) ΔG 9.2 kcal/mol
TS4a as supermolecule         	 -986.477316
TS4c as supermolecule      		 -986.481247
TS5 as  supermolecule          	 -986.487730
TS5 as  separated ions			 -986.474174  (-929.461719 + -57.012455)
Product as supermolecule:        -986.505810  (-910.016541 + -76.471189, ΔG -14.1 kcal/mol)

Water:							  -76.471189
Boric acid						 -252.607946
4,6-dimethyl-1,3,2λ4-
dioxaborinane-2,2-diol anion     -523.927486  
Product as separated ions 	   = -986.490265

Including Two explicit water molecules
NH4(+).2H2O						  -209.954697 (-209.954833 as isolated molecules)
Reactant as separated ions		 -1139.418617 
Reactant as supermolecule		 -1139.421193 (1.6 lower)
TS3 as supermolecule			 -1139.408017 (ΔG 8.27 kcal/mol)

Including Three explicit water molecules
NH4(+(.3H2O)					  -286.426022
Reactant as separated ions		 -1215.889942
Reactant as supermolecule	     -1215.889005
TS3 as supermolecule			 -1215.872507 (ΔG 10.94 kcal/mol)