Carbene formation, hydrogen migration, and fluorescence in the excited states of dialkyldiazirines

Thermal decomposition of iso-propanol: First-principles prediction of total and product-branching rate constants

“…The dissociation of the cpx yields 1 CH 3 CCH 3 ϩH 2 O barrierlessly with an overall endothermocity of 78.2 kcal mol Ϫ1 . The energy difference between the lowest singlet and triplet states (S-T gap͒ of dimethyl carbene ͑DMC͒ is also computed and reported here along with other theoretical 21 results and experimental 22 findings. Our predicted S-T gap is 5.3 kcal/mol in favor of the singlet state, which may be compared with the smaller value 1.64 kcal/mol obtained by Matzinger and Fuelscher 21 at the MRCIϩQ level; they also indicated that the S-T gap might be 1.0-1.5 kcal/mol larger.…”

“…Our predicted S-T gap is 5.3 kcal/mol in favor of the singlet state, which may be compared with the smaller value 1.64 kcal/mol obtained by Matzinger and Fuelscher 21 at the MRCIϩQ level; they also indicated that the S-T gap might be 1.0-1.5 kcal/mol larger. Modarelli et al 22 were able to generate and trap the singlet DMC by laser flash photolysis of dimethyldiazairine and using pyridine as chemical trap, respectively. The reduction of pyridinium ylide's yield upon treatment with oxygen indicated a possible intersystem crossing between the singlet and triplet DMC.…”

Photochemical Reactions in the Synthesis of Protein–Drug Conjugates

“…Synthesis of aliphatic diazirines is straightforward and can be readily accomplished in high yields by using the improved methods reported by Wang et al . As mentioned above, the propensity of aliphatic diazirines to undergo rapid β‐H atom transfer leading to an alkene product, as well as photoinitiated rearrangement to give the diazo isomer which undergoes nucleophilic reactions with the solvent, are major limitations of the photochemistry for bimolecular protein modification . The conformational flexibility of an extended alkyl chain also means that aliphatic carbenes are more likely to undergo intramolecular reactions than the more conformationally rigid aryl carbenes.…”

“…2020,26,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] www.chemeurj.org Concept the photochemistry for bimolecular protein modification. [67,68] The conformational flexibility of an extended alkyl chain also means that aliphatic carbenes are more likely to undergo intramolecular reactions than the more conformationally rigid aryl carbenes.T hese competing intra-and intermolecularp rocesses are likely to restrict the use of aliphatic diazirines to systems that pre-associate.…”

A theoretical investigation into dimethylcarbene and its diamino and diphosphino analogs: effects of cyclization and unsaturation on the stability and multiplicity

“…Presumably, this is due to their ability to undergo rapid intramolecular rearrangements. Evidence has been presented that dimethylcarbene ( 1 CH3 ), the simplest dialkylcarbene, is a true intermediate with a finite lifetime, 21 ns in pentane, at room temperature 8, 9. Earlier theoretical studies on 1 CH3 have been performed only at relatively low levels of theory, calculating its Δ E s–t of 23.810 and 32.2 kcal mol −1 11 at STO‐3G SCF.…”