The carbon

hydrogen

oxygen are the majornitrogen and sulfur atoms

mostly in the form of C-X (X=N

S)

still play a nonnegligible role in the structure and application of coal and oil shale.The homolytic bond dissociation enthalpies (BDE) of C-X for model compounds that are representative of the functionalities present in coal and kerogen were computed by using a double-hybrid method mPW2PLYP.The studies will be helpful for people to construct the transfer model of N and S in pyrolysis

and enrich the knowledge of chemical reaction of typical bonds in coal and kerogen.The BDE for C-N and C-S cover a range from 154.1-55.7 kcal·mol-1 and 83.0-56.6 kcal·mol-1

respectively.The results suggest that the thiophenyl radical or phenylamino radical are the most favorable intermediates in the early pyrolytic stage.With the increase of temperature

the loss of sulfydryl and amidogen groups become feasible

and the ring cleavage reaction of five-membered ring (pyrrole and thiophene) through homolysis of C-N and C-S bond can also occur.The phenyl radical is the most difficult to form

and the directly bond dissociation of C-N bond in pyridine with six-membered ring is extremely unfavorable in the pyrolysis of coal and kerogen.Compared to other types of bonds

C-S bond has the lowest general BDE range.The order of the lowest BDE for various bonds is O-H > C-H > C-C > C-N > C-S > C-O.The bond dissociation of C-O to generate PhOx radical is easier than to generate PhSx radical through homolysis of C-S

otherwise the BDE of C-O is higher than C-S.