Substituent effects in cooperativity of chalcogen bonds

In the present work, substituent effects on cooperativity of S···N chalcogen bonds are studied in XHS···NCHS···4-Z–Py (X = F, Cl; Z = H, F, OH, CH₃, NH₂, NO₂, and CN; and Py = pyridine) complexes using ab initio calculations. An increased attraction or a positive cooperativity is observed on introduction of a third molecule to the XHS···NCHS and NCHS···4-Z–Py binary systems. The shortening of each chalcogen bond distance in the ternary systems is dependent on the substituent Z and is increased in the order Z = NH₂ > OH > CH₃ > H > F > CN > NO₂. The electronic aspects of the complexes are analysed using molecular electrostatic potential, and the parameters derived from the atoms in molecules and natural bond orbital methodologies. According to interaction energy decomposition analysis, the electrostatic energies are important in the interaction energy of S···N bonds and may be regarded as being responsible for the stability of these complexes.     

N4H4分子取代基效应的量子化学研究

本文计算了甲基(-CH3),羟基（-OH）对1-丁氮烯和2-丁氮烯的取代基效应。当1-丁氮烯引入取代基后,N=N双键的键长变短,而N-N单键的键长增长。异构体2-丁氮烯的键长变化较小。当引入甲基或羟基后,N原子的孤对电子会与相应的N-C(N-O)键之间发生相互作用,使整个分子的超共轭作用增强。随着取代基数目的增多,总能量和生成热就会降低,取代基数目与分子能量（生成热）之间具有很好的相关性。     

苯乙酮类化合物的碳谱研究

本文分析了九个被羟基和和（或）甲氧基取代的苯乙酮类化合物的碳谱数据，首次提出了理论计算这类化合物芳环碳化学位移的计算公式以及羟基和甲氧基的取代参数。羟基的取代参数分别为：３０．４（Ｚ），－１３．２（Ｚ）（Ｚｍ）和－７．８（Ｚｐ），甲氧基的取代参数分别为：３０．５（Ｚｉ），－１４．１（Ｚｏ），０．６（Ｚｍ）和－７．２（Ｚｐ）。计算公式分别为：δＣ１＝１３７．３＋ΣＺδＣ４＝１３３．０＋ΣＺresume     

Substituent effect on azobenzene‐based liquid‐crystalline organophosphorus polymers

An Erratum has been published for this article in Journal of Polymer Science Part A: Polymer Chemistry (2003) 41(23) 3862 A new series of combined‐type, azobenzene‐based organophosphorus liquid‐crystalline polymers were synthesized, and their photoisomerization properties were studied. The prepared polymers contained azobenzene units as both the main‐chain and side‐chain mesogens. Various groups were substituted in the terminal of the side‐chain azobenzene mesogen, and the effects of the substituents were investigated. All the polymers were prepared at the ambient temperature by solution polycondensation with various 4‐substituted phenylazo‐4′‐phenyloxyhexylphosphorodichloridates and 4,4′‐bis(6‐hydroxyhexyloxy) azobenzene. The polymers were characterized with gel permeation chromatography, Fourier transform infrared, and ¹H, ¹³C, and ³¹P NMR spectroscopy. Thermogravimetric analysis revealed that all the polymers had high char yields. The liquid‐crystalline behavior of the polymers was examined with hot‐stage optical polarizing microscopy, and all the polymers showed liquid‐crystalline properties. The formation of a mesophase was confirmed by differential scanning calorimetry (DSC). The DSC data suggested that mesophase stability was better for electron‐withdrawing substituents than for halogens and unsubstituted ones. Ultraviolet irradiation studies indicated that the time taken for the completion of photoisomerization depended on the dipolar moment, size, and donor–acceptor characteristics of the terminal substituents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3188–3196, 2003     

Substituent effect of large conjugate groups on the DNA base pair derivatives: Density functional study

The substituent effects caused by 2‐nitro‐naphthalen (aNO₂), 2‐hydroxyl‐naphthalen (aOH), 1‐nitro‐4‐vinyl‐benzene (bNO₂), and 1‐hydroxyl‐4‐vinyl‐benzene (bOH) have been investigated in this report. The geometries of various substituted base pairs have been optimized using the B3LYP method at the 6‐31G* level with no constraints. The vertical ionization potential energy has been calculated. Natural bond orbital (NBO) and CHelp analyses have also been carried out on both the neutral and cationic systems at the same level. The outcomes show that the hydrogen bond lengths of these substituted base pairs are similar to unsubstituted bases, while the geometries of the substituted bases have an interesting aspect; i.e., the substituent and the substituted base are nonplanar when the substituted base is pyrimide, while it is coplanar when the substituted base is purine. The stabilization energies changed slightly as compared with the corresponding A:T or G:C base pairs. NBO analysis shows that charge transfer is the largest in aOH‐T:A, while it is small in the other derivatives. Population analysis shows that the NPA and Mulliken charge of H has a relationship with the H‐bond lengths, while that of Chelp does not. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Substituent effect on ionisation potential in a series of related molecules: A theoretical study in a molecular orbital framework

The effect of replacing the hydrogen atoms in thioformaldehyde by halogen atoms (F, Cl) on the ionisation potential of the non-bonding electron is analysed by using the Hellman-Feynman theorem, regarding the nuclear charge of the substituent as a parameter in the many-electron Hamiltonian. The trends predicted by our theory nicely agree with the relevant ionisation potentials computed either by applying Koopmans’ theorem or by the ΔE _SCF method. For the carbonyls, avaible experimental data indicate the reliability of our prediction.     

对(mèng)烷的~(13)C-NMR研究顺反异构体比及顺式构象平衡常数K(35℃)

本工作是在35℃下测定对(艹孟)烷(p-Menthane)(即对位甲基异丙基环已烷)的~(13)C-NMR谱。由取代基参数,经验加和规律计算各碳化学位移数值,归属各谱峰位置。由积分值得知顺式、反式对(艹孟)烷含量之比。并根据权分法计算顺式对(艹孟)烷中构象1与构象2分子数之比。结果表明顺式对(艹孟)烷中异丙基处于平展位置的构象2为主。     

8-羟基喹啉锂的光电性能和取代基效应的密度泛函理论

采用密度泛函理论(DFT)较为系统地研究了给、吸电子取代基对8-羟基喹啉锂(Liq)光电性能的影响。研究结果表明:不同取代基与母体形成不同的共轭,取代基—CN、—OCH3很好地参与了整个π体系共轭,对体系性质影响较大;吸电子基—CF3、—CN、—Cl在5-位取代都使Liq的最高占据轨道(HOMO)、最低空轨道(LUMO)能级降低;给电子基—CH3、—CH3CH2CH2、—OCH3在5-位取代都使Liq的LUMO、HOMO升高,带隙减小,给电性越强,影响越显著;—CN在5-位取代,显著增加了Liq的电子亲和势,降低了电子重组能,使电子更易于注入和传输。与Liq及其它衍生物相比,5-CN-Liq是一种更好的电子注入和传输材料。