Substituent effects on CL···N, S···N, and P···N noncovalent bonds

Cl, S, and P atoms have previously been shown as capable of engaging in a noncovalent bond with the N atom on another molecule. The effects of substituents B on the former atoms on the strength of this bond are examined, and it is found that the binding energy climbs in the order B = CH(3) < NH(2) < CF(3) < OH < Cl < NO(2) < F. However, there is some variability in this pattern, particularly for the NO(2) group. The A···N bonds (A = Cl, S, P) can be quite strong, amounting to as much as 10 kcal/mol. The binding energy arises from approximately equal contributions from its induction and electrostatic components, although the former becomes more dominant for the stronger bonds. The induction energy is due in large measure to the transfer of charge from the N lone pair to a B-A σ* antibonding orbital of the electron-acceptor molecule containing Cl, S, or P. These A···N bonds typically represent the lowest-energy structure on each potential energy surface, stronger than H-bonds such as NH···F, CH···N, or SH···N.     

Weak H-bonds. Comparisons of CH···O to NH···O in proteins and PH···N to direct P···N interactions

Whereas CH···O H-bonds are usually weaker than interpeptide NH···O H-bonds, this is not necessarily the case within proteins. The nominally weaker CH···O are surprisingly strong, comparable to, and in some cases stronger than, the NH···O H-bonds in the context of the forces that hold together the adjacent strands in protein β-sheets. The peptide NH is greatly weakened as proton donor in certain conformations of the protein backbone, particularly extended structures, and forms correspondingly weaker H-bonds. The PH group is a weak proton donor, but will form PH···N H-bonds. However, there is a stronger interaction in which P can engage, in which the P atom, not the H, directly approaches the N electron donor to establish a direct P···N interaction. This approach is stabilized by the same sort of electron transfer from the N lone pair to the P-H σ* antibond that characterizes the PH···N H-bond.     

C-H···π interactions in the CHBrF2···HCCH weakly bound dimer

The microwave spectra of four isotopologues of the CHBrF(2)···HCCH weakly bound dimer have been measured in the 6-18 GHz region using chirped-pulse and Balle-Flygare Fourier-transform microwave spectroscopy. Spectra of (13)CH(79)BrF(2) and (13)CH(81)BrF(2) monomers have also been measured, and spectroscopic constants are reported. Measurement of spectra for the (79)Br and (81)Br isotopologues of CHBrF(2) complexed with both (12)C(2)H(2) and (13)C(2)H(2) have allowed the determination of a structure with C(s) symmetry for this complex. CHBrF(2) interacts with the triple bond of acetylene via a C-H···π contact (R(H···π) = 2.670(8) ?) with the Br atom lying in the ab plane, located 3.293(40) ? from a hydrogen atom of the HCCH molecule. The structure of CHBrF(2)···HCCH has been compared with recently studied related acetylene complexes, including a comparison with (and further structural analysis of) the CHClF(2)···HCCH complex.     

Competition between H···π and H···O interactions in furan heterodimers

Here the interactions of furan with HZ (Z = CCH, CCF, CN, Cl, and F) are studied using a variety of electron correlation methods (MP2, CCSD(T), DFT-SAPT) and correlation-consistent triple- and quadruple-ζ basis sets including complete basis set (CBS) extrapolation. For Fu-HF all methods agree that a n-type structure with a hydrogen bridge between the oxygen lone-pair of furan and the hydrogen atom of HF is the global minimum structure. It is found to be significantly more stable than a π-type structure where the hydrogen atom of HF points toward the π system of furan. For the other four dimers MP2 and DFT-SAPT predict the π-type structure to be somewhat more stable, while CCSD(T) favors the n-type structure as the global minimum for Fu-HCl and predicts both structures as nearly isoenergetic for Fu-HCCH and Fu-HCCF. From a geometrical point of view, the Fu-HCN dimer structures are more related to those of the Fu-HCl complex than to Fu-HCCH. The different behavior of HCCF and HF upon complexation with furan evidence the effect of the presence of a π system in the aggregation of fluorine derivatives. It is shown that aggregates of furan cannot be understood by means of dipole-dipole and electrostatic analysis only. Yet, through a combined and detailed analysis of DFT-SAPT energy contributions and resonance effects on the molecular charge distributions a consistent explanation of the aggregation of furan with both π electron rich molecules and halogen hydrides is provided.     

·亮点介绍·

新型离去基团:1,3-二羰基Angew.Chem.Int.Ed.2011,50,2975～2978有机合成化学中的反应(除重排反应)通常不涉及到C—C键的骨架变化.探索C—C键选择性切断及其反应规律,发展C—C键活化的新模式,成为有机合成化学中非常具有挑战性的研究课题。     

SH···N and SH···P blue-shifting H-bonds and N···P interactions in complexes pairing HSN with amines and phosphines

Quantum calculations at the MP2/aug-cc-pVDZ level examine complexes pairing HSN with aliphatic amines and phosphines. Complexes are cyclic and contain two attractive interactions. The first is a SH···N/P H-bond in which the S-H covalent bond contracts and shifts its stretching frequency to the blue, more so for amines than for phosphines. The second interaction is different for the amines and phosphines. The amines engage in a NH···N H-bond comparable in strength to the aforementioned SH···N interaction. In contrast, the second interaction in the phosphine complexes is a direct N···P attraction without an intervening H. This interaction is due in part to opposite partial charges on the N and P atoms, as well as covalent forces generated by charge transfer effects.     

·读者园地·

问 :1 .在燃烧法测定碳的气路中 ,对放置在除尘管中的过滤棉有什么要求 ?2 .怎样合理使用燃烧炉瓷管 ?3.对气体容量定碳仪的气密性有何要求 ?——湖南作者　　张林　　　　答 1 :通常除尘管为一直径 1 0～ 1 5mm,长 80～ 1 0 0 mm的玻璃滤气管 ,管内充塞适量脱脂棉 (近燃烧管一端塞少许石棉 ,以防火星溅入致使棉花着火 )或玻璃棉以滤除金属氧化物粉尘。所用脱脂棉应干燥 ,因为潮湿的棉花会吸留少量 CO2 。若使用玻璃棉时 ,应事先将其用盐酸浸煮 ,然后洗净烘干。否则会因玻璃棉带有碱性而吸收 CO2 ,使测定结果发生错误。工作过程中还应经…     

Structure of 7-azaindole···2-fluoropyridine dimer in a supersonic jet: competition between N-H···N and N-H···F interactions

In the present work, we have investigated the structure of 7-azaindole···2-fluoropyridine dimer in a supersonic jet by employing resonant two photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. The R2PI spectrum of the dimer is recorded by electronic excitation of the 7-azaindole moiety, and a few low frequency intermolecular vibrations of the dimer are clearly observed in the spectrum. The electronic origin band of the dimer is red-shifted by 1278 cm(-1) from the S(1) ← S(0) origin band of 7-azaindole monomer. The presence of a single conformer of the dimer is confirmed by IR-UV and UV-UV hole-burning spectroscopic techniques. RIDIR (Resonant ion dip infrared) spectrum of the dimer shows a red-shift of 265 cm(-1) in the N-H stretching frequency with respect to that of the 7-azaindole monomer. Two planar double hydrogen bonded cyclic structures of the dimer have been predicted from DFT calculations. Comparison of experimental and theoretical N-H stretching frequencies confirms that the observed dimer is stabilized by N-H···N and C-H···N hydrogen bonding interactions. The less stable conformer with N-H···F and C-H···N interactions are not observed in the experiment. The competition between N-H···N and N-H···F interactions in the two dimeric structures are discussed from natural bond orbital (NBO) analysis. The current results demonstrate that fluorine makes a hydrogen bond of intermediate strength through cooperative interaction of another hydrogen bond (C-H···N) present in the dimer, although fluorine is believed to be very weak hydrogen bond acceptor.     

Noncovalent functionalization of graphene via π-hole···π and σ-hole···π interactions

Physisorption of bromopentafluorobenzene (C₆F₅Br) on graphene can occur due to the unique σ-hole and π-hole characters of C₆F₅Br and the rich π-electrons region of graphene, leading to the formation of three types of π-hole···π and σ-hole···π interactions. The π-hole···π interactions are even stronger than the σ-hole···π interactions. The property of graphene was significantly affected by such physisorption.

     

XH···HOCl···YH体系中氢键与卤键协同效应的理论研究

采用MP2方法在6-311++G(d,p)基组水平上对三分子体系XH…HOCl…YH(X=F,Cl,Br,OH;Y=F,Cl,Br,OH,NH2)中氢键和卤键之间的协同效应进行了研究。研究过程中计算了二体XH…HOCl中氢键,二体HOCl…YH中卤键和三体XH…HOCl…YH中氢键和卤键的键长、分子间的相互作用能以及它们的振动频率。发现和二体相比,三体中氢键和卤键的键长缩短,分子间的相互作用能增大,振动频率增大。再通过AIM分析,比较了二体、三体中氢键和卤键键鞍点处电子密度强弱的变化,结果电子密度在三体中明显增大,分析结果还显示氢键和卤键属于分子间弱相互作用的范畴,它们的静电作用和二体相比也有所增强。这些现象都表明三体中氢键和卤键之间存在正的协同效应。     

Cooperativity between S···π and Rg···π in the OCS···C6H6···Rg (Rg = He, Ne, Ar, and Kr) van der Waals complexes

The complexes OCS···C(6)H(6), C(6)H(6)···Rg, and OCS···C(6)H(6)···Rg (Rg = He, Ne, Ar, and Kr) have been studied by means of MP2 calculations and QTAIM analyses. The optimized geometries of the title complexes have C(6v) symmetry. The intermolecular interactions in the OCS···C(6)H(6)···Rg complexes are comparatively stronger than that in the OCS···C(6)H(6) complex, which prove that the He, Ne, Ar, and Kr atoms have the ability to form weak bonds with the benzene molecule. In QTAIM studies, the π-electron density of benzene was separated from the total electron density. The molecular graphs and topological parameters of the OCS···πC(6)H(6), πC(6)H(6)···Rg, and OCS···πC(6)H(6)···Rg complexes indicate that the interactions are mainly attributed to the electron density provided by the π-bonding electrons of benzene and the top regions of the S and Rg atoms. Charge transfer is observed from the benzene molecule to SCO/Rg in the formation of the OCS···C(6)H(6), C(6)H(6)···Rg, and OCS···C(6)H(6)···Rg complexes. Molecular electrostatic potential (MEP) analyses suggest that the electrostatic energy plays a pivotal role in these intermolecular interactions.     

Microwave spectroscopic and theoretical studies on the phenylacetylene···H2O complex: C-H···O and O-H···π hydrogen bonds as equal partners

Rotational spectra of five isotopologues of the title complex, C(6)H(5)CCH···H(2)O, C(6)H(5)CCH···HOD, C(6)H(5)CCH···D(2)O, C(6)H(5)CCH···H(2)(18)O and C(6)H(5)CCD···H(2)O, were measured and analyzed. The parent isotopologue is an asymmetric top with κ = -0.73. The complex is effectively planar (ab inertial plane) and both 'a' and 'b' dipole transitions have been observed but no c dipole transition could be seen. All the transitions of the parent complex are split into two resulting from an internal motion interchanging the two H atoms in H(2)O. This is confirmed by the absence of such doubling for the C(6)H(5)CCH···HOD complex and a significant reduction in the splitting for the D(2)O analog. The rotational spectra, unambiguously, reveal a structure in which H(2)O has both O-H···π (π cloud of acetylene moiety) and C-H···O (ortho C-H group of phenylacetylene) interactions. This is in agreement with the structure deduced by IR-UV double resonance studies (Singh et al., J. Phys. Chem. A, 2008, 112, 3360) and also with the global minimum predicted by advanced electronic structure theory calculations (Sedlack et al., J. Phys. Chem. A, 2009, 113, 6620). Atoms in Molecule (AIM) theoretical analysis of the complex reveals the presence of both O-H···π and C-H···O hydrogen bonds. More interestingly, based on the electron densities at the bond critical points, this analysis suggests that both these interactions are equally strong. Moreover, the presence of both these interactions leads to significant deviation from linearity of both hydrogen bonds.     

Rapid and accurate evaluation of the binding energies and the individual N-H···O=C, N-H···N, C-H···O=C, and C-H···N interaction energies for hydrogen-bonded peptide-base complexes

The binding energies of thirty-six hydrogen-bonded peptide-base complexes, including the peptide backbone-ase complexes and amino acid side chain-base complexes, are evaluated using the analytic potential energy function established in our lab recently and compared with those obtained from MP2, AMBER99, OPLSAA/L, and CHARMM27 calculations. The comparison indicates that the analytic potential energy function yields the binding energies for these complexes as reasonable as MP2 does, much better than the force fields do. The individual N H…O=C, N H…N, C H…O=C, and C H…N attractive interaction energies and C=O…O=C, N H…H N, C H…H N, and C H…H C repulsive interaction energies, which cannot be easily obtained from ab initio calculations, are calculated using the dipole-dipole interaction term of the analytic potential energy function. The individual N H…O=C, C H…O=C, C H…N attractive interactions are about 5.3±1.8, 1.2±0.4, and 0.8 kcal/mol, respectively, the individual N H … N could be as strong as about 8.1 kcal/mol or as weak as 1.0 kcal/mol, while the individual C=O…O=C, N H…H N, C H…H N, and C H…H C repulsive interactions are about 1.8±1.1, 1.7±0.6, 0.6±0.3, and 0.35±0.15 kcal/mol. These data are helpful for the rational design of new strategies for molecular recognition or supramolecular assemblies.     

Cooperative and diminutive unusual weak bonding in F3CX···HMgH···Y and F3CX···Y···HMgH trimers (X = Cl, Br; Y = HCN, and HNC)

MP2 calculations with cc-pVTZ basis set were used to analyze intermolecular interactions in F(3)CX···HMgH···Y and F(3)CX···Y···HMgH triads (X = Cl, Br; Y = HCN, and HNC) which are connecting with three kinds of unusual weak interactions, namely halogen-hydride, dihydrogen, and σ-hole. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads were investigated at the MP2/cc-pVTZ computational level. Particular attention is given to parameters such as cooperative energies, cooperative dipole moments, and many-body interaction energies. Those complexes with simultaneous presence of a σ-hole bond and a dihydrogen bond show cooperativity energy ranging between -1.02 and -2.31 kJ mol(-1), whereas those with a halogen-hydride bond and a dihydrogen bond are diminutive, with this energetic effect between 0.1 and 0.63 kJ mol(-1). The electronic properties of the complexes have been analyzed using the molecular electrostatic potential (MEP), the electron density shift maps, and the parameters derived from the atoms in molecules (AIM) methodology.     

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毛主席教导我们:“我们的报纸也要靠大家来办,靠全体人民群众来办,靠全党来办,而不能只靠少数人关起门来办。”在毛主席的革命路线指引下,在党的领导下,《化学通报》复刊以来,得到了各有关部门、工厂、农村、部队、学校、科研单位以及广大读者的热情关怀和大力支持。不少读者来信给予了鼓励和希望,提出了批评和建议。对于读者的宝贵意见,我们表示衷心的感谢和热烈的欢迎,并予以认真研     

读者·作者·编者

《化学分析计量》入选美国《化学文摘》(CA)千种表根据中国高等学校自然科学学报研究会资料,美国《化学文摘》数据库总计10000种以上期刊,中国期刊已超过1412种;引文频次最高的1000种期刊表中,收录中国(含港台)期刊236种,其中《化学分析计量》在千种表中排名第772。我们将一