The crystal structure of (4S)-5-(2-methoxy-2-oxoethylamino)-5-oxo-4-(3,4,5- trimethoxybenzamido) pentanoic acid 5 (C18H24N2O9, Mr = 412.39) has been determined by single- crystal X-ray diffraction analysis. The crysta...The crystal structure of (4S)-5-(2-methoxy-2-oxoethylamino)-5-oxo-4-(3,4,5- trimethoxybenzamido) pentanoic acid 5 (C18H24N2O9, Mr = 412.39) has been determined by single- crystal X-ray diffraction analysis. The crystal belongs to monoclinic, space group P21/c with a = 27.665(9), b = 5.1444(16), c = 13.907(4) ?, β = 98.401(5)o, V = 1958.0(11) ?3, Z = 4, Dc = 1.399 g/cm3, μ = 0.113 mm-1, F(000) = 872, R = 0.0606 and wR = 0.1405 (I > 2σ(I)). The results con- firmed that 5 could be assigned to the tautomeric form. The intermolecular hydrogen bonds between O(5)–H(5)…O(7), N(2)–H(2)…O(6) and N(1)–H(1)…O(4) have been observed.展开更多
All four isomers of a novel fl-branched unusual amino acid were designed and synthesized with high stereoselectivity （〉 90% de） and in 33%--44% overall yields by the use of 4（R/S）-5,5-dimethyl-4-phenyl-oxazolidin...All four isomers of a novel fl-branched unusual amino acid were designed and synthesized with high stereoselectivity （〉 90% de） and in 33%--44% overall yields by the use of 4（R/S）-5,5-dimethyl-4-phenyl-oxazolidin-2-one as the chiral auxiliary via asymmetric 1,4-Michael addition, direct or indirect azidation, hydrolysis and hydrogenation reactions.展开更多
Methyl pentanoate(MP)was identified as a potential candidate.To facilitate the application of MP with high efficiency in engines,a comprehensive understanding of combustion chemical kinetics of MP is necessary.In this...Methyl pentanoate(MP)was identified as a potential candidate.To facilitate the application of MP with high efficiency in engines,a comprehensive understanding of combustion chemical kinetics of MP is necessary.In this work,the H-abstraction reactions from MP by H and CH_(3) radicals,critical in controlling the initial fuel consumption,are theoretically investigated at the DLPNO-CCSD(T)/CBS(T-Q)//M06-2X/cc-pVTZ level of theory.The multistructural torsional(MS-T)anharmonicity is characterized using the dual-level MS-T method;the HF/3-21G and M06-2X/cc-pVTZ methods are chosen as the low-and high-level methods,respectively.The conventional transition state theory(TST)is employed to calculate the high-pressure limit rate constants at 298-2000 K with the Eckart tunneling correction.Our calculations indicate that the hydrogen atoms of the methylene functional group are easier to be abstracted by H and CH_(3) radicals.The multistructural torsional anharmonicities of H-abstraction reactions MP+H/CH_(3) are significant within the temperature range investigated.The tunneling effects are more pronounced at low temperatures,and contribute considerably to the rate constants below 500 K.The model from the work of Diévart et al.is updated with our calculations,and the simulations of the updated model are in excellent agreement with the reported ignition delay time of MP/O2/Ar and MP/Air mixtures.The sensitivity analysis indicates that the H-abstraction reactions,MP+H-CH_(3)CH_(2)CHCH_(2)C(-O)OCH_(3)/CH_(3)CHCH_(2)CH_(2)C(-O)OCH_(3)+H2,are critical in controlling the initial fuel consumption and ignition delay time of MP.展开更多
基金The project was supported by the National Natural Science Foundation of China (No. 20272033) and the Doctoral Foundation of Ministry of Education of China (No. 20020422024)
文摘The crystal structure of (4S)-5-(2-methoxy-2-oxoethylamino)-5-oxo-4-(3,4,5- trimethoxybenzamido) pentanoic acid 5 (C18H24N2O9, Mr = 412.39) has been determined by single- crystal X-ray diffraction analysis. The crystal belongs to monoclinic, space group P21/c with a = 27.665(9), b = 5.1444(16), c = 13.907(4) ?, β = 98.401(5)o, V = 1958.0(11) ?3, Z = 4, Dc = 1.399 g/cm3, μ = 0.113 mm-1, F(000) = 872, R = 0.0606 and wR = 0.1405 (I > 2σ(I)). The results con- firmed that 5 could be assigned to the tautomeric form. The intermolecular hydrogen bonds between O(5)–H(5)…O(7), N(2)–H(2)…O(6) and N(1)–H(1)…O(4) have been observed.
基金Project supported by the National Natural Science Foundation of China （Nos. 20472071, 20562014 and 30860342） and Natural Science Foundation of Yunnan Province （No. 2009cc017）.
文摘All four isomers of a novel fl-branched unusual amino acid were designed and synthesized with high stereoselectivity （〉 90% de） and in 33%--44% overall yields by the use of 4（R/S）-5,5-dimethyl-4-phenyl-oxazolidin-2-one as the chiral auxiliary via asymmetric 1,4-Michael addition, direct or indirect azidation, hydrolysis and hydrogenation reactions.
基金This work was supported by the National Natural Science Foundation of China(Nos.201903064,11627901).
文摘Methyl pentanoate(MP)was identified as a potential candidate.To facilitate the application of MP with high efficiency in engines,a comprehensive understanding of combustion chemical kinetics of MP is necessary.In this work,the H-abstraction reactions from MP by H and CH_(3) radicals,critical in controlling the initial fuel consumption,are theoretically investigated at the DLPNO-CCSD(T)/CBS(T-Q)//M06-2X/cc-pVTZ level of theory.The multistructural torsional(MS-T)anharmonicity is characterized using the dual-level MS-T method;the HF/3-21G and M06-2X/cc-pVTZ methods are chosen as the low-and high-level methods,respectively.The conventional transition state theory(TST)is employed to calculate the high-pressure limit rate constants at 298-2000 K with the Eckart tunneling correction.Our calculations indicate that the hydrogen atoms of the methylene functional group are easier to be abstracted by H and CH_(3) radicals.The multistructural torsional anharmonicities of H-abstraction reactions MP+H/CH_(3) are significant within the temperature range investigated.The tunneling effects are more pronounced at low temperatures,and contribute considerably to the rate constants below 500 K.The model from the work of Diévart et al.is updated with our calculations,and the simulations of the updated model are in excellent agreement with the reported ignition delay time of MP/O2/Ar and MP/Air mixtures.The sensitivity analysis indicates that the H-abstraction reactions,MP+H-CH_(3)CH_(2)CHCH_(2)C(-O)OCH_(3)/CH_(3)CHCH_(2)CH_(2)C(-O)OCH_(3)+H2,are critical in controlling the initial fuel consumption and ignition delay time of MP.
