三烃基锡配合物（PhCMe2CH2）3Sn[O2C（CHRPh）][R：OH（1）, H（2）]的合成、结构、热稳定性、量子化学及毒性研究

甲醇中氧化双[三（2-甲基-2-苯基）丙基锡]分别与DL-扁桃酸、苯乙酸反应,合成了2个三烃基锡配合物（PhCMe₂CH₂）₃Sn[O₂CCH（OH）Ph]（1）和（PhCMe₂CH₂）₃Sn（O₂CCH₂Ph）（2）。经IR、¹H和¹³CNMR、元素分析和X-射线单晶衍射表征结构。1和2均属三斜晶系,空间群P1。配合物1晶体学参数：a=0.9711（2）nm,b=1.1766（3）nm,c=1.7008（4）nm,α=96.840（12）°,β=103.235（12）°,γ=110.725（11）°,Z=2,V=1.7260（7）nm³,D_c=1.288g·cm^-3,μ（MoKα）=0.773mm^-1,F（000）=696,R₁=0.0325,wR₂=0.0873。配合物2晶体学参数：a=0.97285（9）nm,b=1.16140（11）nm,c=1.68931（16）nm,α=96.830（5）°,β=101.935（5）°,γ=110.770（4）°,Z=2,V=1.7071（3）nm³,D_c=1.271g·cm^-3,μ（MoKα）=0.778mm^-1,F（000）=680,R₁=0.0248,wR₂=0.0673。1和2的中心锡原子均为畸变四面体构型。通过分子间C-H…O或C-H…π作用,1和2分别形成一维带状或链状结构。热重分析结果表明,1和2具有良好的稳定性。毒性测试的初步结果表明,配合物1、2具有较好的环境相容性,对石螺急性毒性较小。     

5, 5’-二硫双（2-硝基苯甲酸）构筑的钴配合物的合成与晶体结构

以柔性配体5,5’-二硫双（2-硝基苯甲酸）为主配体,与含氮辅助配体在水热条件下合成了2个Co（Ⅱ）配合物{[Co（dtb）（bpp）·H₂O]}_n（1）,{[Co（dtb）（phen）·2H₂O]}_n（2）（H₂dtb=5,5’-二硫双（2-硝基苯甲酸）,phen=1,10-菲咯啉,bpp=1,3-二（4-吡啶）-丙烷）,通过X-射线单晶衍射、X-射线粉末衍射、红外光谱、热重分析和元素分析方法对其进行表征。结构测试表明1为正交晶系,Pbca空间群,晶胞参数为a=1.0149（2）nm,b=2.2159（5）nm,c=2.5291（6）nm,V=5.688（2）nm³,D_c=1.564g·cm^-3,Z=8。2为三斜晶系,P1空间群,晶胞参数为a=0.7401（3）nm,b=1.0742（4）nm,c=1.7837（6）nm,α=98.452（7）°,β=99.816（7）°,γ=98.979（7）°,V=1.3580（8）nm³,D_c=1.637g·cm^-3,Z=2。化合物1为三维网络结构,并包含单股双轴假螺旋结构。配合物2为一维链状结构,相邻一维链之间通过氢键作用形成二维超分子网络结构。     

三个基于3-(2，5-二羧基苯基)-吡啶羧酸的Cu(Ⅱ)、Mn(Ⅱ)配合物的结构及磁性

通过水热法合成了3个新型配位聚合物：[Cu（Hdppa）（H₂O）]_n（1）、{[Cu₂（dppa）（μ₂-OH）（H₂O）]·H₂O}_n（2）和{[Mn₃（dppa）₂（H₂O）₄]·2H₂O}_n（3）,（H₃dppa=3-（2,5-二羧基苯基）-吡啶羧酸）,并对其进行了元素分析、红外光谱、粉末X射线衍射和热重分析表征。X射线单晶衍射分析结果表明：化合物1属于单斜晶系,P2₁/c空间群,a=1.371（2）nm,b=0.805（11）nm,c=1.266（19）nm,β=112.74（3）°,Z=4;化合物2属于三斜晶系,P1空间群,a=0.839（4）nm,b=1.039（5）nm,c=1.110（5）nm,α=98.31°,β=110.630（3）°,γ=111.90（3）°,Z=2;化合物3属于三斜晶系,P1空间群,a=0.881（6）nm,b=0.939（6）nm,c=1.038（7）nm,α=100.29°,β=97.990（10）°,γ=111.13（7）°,Z=1。化合物1以配体Hdppa^2-桥联Cu（Ⅱ）形成一维链状结构;化合物2和3以配体dppa^3-分别桥联Cu（Ⅱ）和Mn（Ⅱ）形成二维层状结构,并进一步通过氢键形成三维超分子结构。变温磁化率研究表明在化合物1和化合物2中存在较强的铁磁耦合作用,其磁交换常数分别为4.44和8.94 cm^-1;而化合物3中Mn（Ⅱ）离子之间存在反铁磁相互作用。     

基于2, 5-二甲基苯-1, 4-二亚甲基二膦酸的钴、镍同构化合物的水热合成及晶体结构

在水热条件下,利用2,5-二甲基苯-1,4-二亚甲基二膦酸（H₄L）与CoCl₂·6H₂O或NiSO₄·6H₂O反应得到2个同构的过渡金属有机膦酸化合物,[Co（H₂O）₄（H₂L）]_n（1）,[Ni（H₂O）₄（H₂L）]_n（2）,并用元素分析、红外光谱、粉末及单晶X-射线等方法对其进行了表征。晶体结构分析表明：化合物1和2都属于三斜晶系,空间群为P1,化合物1的晶胞参数为a=0.4970（2）nm,b=0.7113（3）nm,c=1.1778（5）nm,α=97.779（7）°,β=92.103（7）°,γ=107.217（6）°,V=0.3927（3）nm³,Z=2;化合物2的晶胞参数为a=0.49435（19）nm,b=0.7089（3）nm,c=1.1726（5）nm,α=97.919（6）°,β=92.130（6）°,γ=107.441（5）°,V=0.3870（3）nm³,Z=2。金属离子采取了八面体构型,6个配位氧原子分别来自2个反式构型的H₂L配体和4个配位水分子。每1个金属离子与2个反式构型的H₂L配体配位形成了一维线型链状结构。这2个化合物最终通过O-H…O氢键作用形成了三维结构。此外,对2个化合物的热稳定性也进行了研究。     

基于3, 3’, 5, 5’-(1, 3-苯基)-联苯四羧酸构筑的两个配位聚合物的合成、晶体结构和荧光性质

以3,3’,5,5’-（1,3-苯基）-联苯四羧酸（H₄btb）与1,10-菲咯啉（phen）为配体,分别与硝酸镉和硝酸锌在水热条件下反应合成2个一维[Cd（H₂btb）（phen）]_n（1）和二维{[Zn₂（btb）（phen）]·1.5H₂O}_n（2）配位聚合物,并对其进行了元素分析、红外光谱、热重分析和X-射线单晶衍射测定。配合物1属于单斜晶系,空间群为C2/c,晶胞参数：a=2.82845（13）nm,b=1.08554（5）nm,c=1.81768（8）nm,β=96.4850（10）°,V=5.5453（4）nm³,Z=8,D_c=1.670Mg·m^-3,F（000）=2800,R₁=0.0339,wR₂=0.0718[I >2σ（I）],配体H₄btb的2个羧基分别采取μ₁-η¹：η¹、μ₂-η²：η¹配位模式连接镉原子形成一维带状结构。化合物2也属于单斜晶系,空间群为P2₁/c,晶胞参数：a=1.7471（3）nm,b=1.2511（2）nm,c=2.1870（3）nm,β=120.911（11）°,V=4.1014（11）nm³,Z=4,D_c=1.491Mg·m^-3,F（000）=1876,R₁=0.0673,wR₂=0.1749[I>2σ（I）],全部去质子的H₄btb配体的4个羧基分别采取μ₁-η¹：η⁰、μ₁-η¹：η¹、μ₂-η¹：η¹配位模式连接锌原子形成一维链,链间通过μ₂-η¹：η¹桥连羧基扩展为（3,5）-连接的二维（4²·6⁷·8）（4²·6）网状结构。同时研究了2个配合物的荧光性质。     

三(3,5-二氟苄基)氯化锡和四(邻氯苄基)锡的合成、晶体结构及量子化学

3,5-二氟苄基氯和邻氯基苄基氯在适当的溶剂中与锡粉反应,合成了三（3,5-二氟苄基）氯化锡（1）和四（邻氯苄基）锡（2）,经X射线衍射方法测定了新化合物的晶体结构。化合物1属单斜晶系,空间群为C2/c,晶体学参数：a=1.858 33（11）nm,b=1.140 98（7）nm,c=2.690 06（16）nm,β=109.288（10）°,V=5.383 6（6）nm³,Z=8,D_c=1.532 g·cm^-3,μ（Mo Kα）=13.61 cm^-1,F（000）=2 480,R₁=0.085 1,wR₂=0.168 1。化合物2属单斜晶系,空间群为P2₁/m,晶体学参数：a=0.585 54（5）nm,b=1.969 74（18）nm,c=0.857 86（8）nm,β=95.204 0（10）°,V=0.985 34（15）nm³,Z=2,D_c=1.805 g·cm^-3,μ（Mo Kα）=14.91 cm^-1,F（000）=524,R₁=0.054 0,wR₂=0.163 9;中心锡原子为畸变四面体构型。对其结构进行量子化学从头计算,探讨了化合物的稳定性、分子轨道能量以及部分前沿分子轨道的组成特征。测定了化合物的热稳定性。     

两个三环己基锡芳香羧酸酯的合成、结构、热稳定性及体外抗癌活性研究

甲醇中三环己基氢氧化锡分别与呋喃-2-甲酸、2,4,6-三甲基苯甲酸反应,合成了2个三环己基锡芳香羧酸酯Cy₃SnO₂CC₄H₃O（1）和Cy₃SnO₂CC₆H₂Me₃（2）（Cy为环己基）。通过IR、¹H和¹³C NMR、元素分析及X-射线单晶衍射表征结构。（1）和（2）均属单斜晶系,配合物（1）空间群P2₁,晶体学参数：a=0.82304（2）nm,b=1.11119（3）nm,c=1.28390（3）nm,β=101.090（2）°,Z=2,V=1.15227（5）nm³,D_c=1.381g·cm^-3,μ（Mo Kα）=1.127mm^-1,F（000）=496,R₁=0.0529,wR₂=0.1387。配合物（2）空间群P2₁/c,晶体学参数：a=0.99962（2）nm,b=1.41597（2）nm,c=1.97359（3）nm,β=94.0420（10）°,Z=4,V=2.78653（8）nm³,D_c=1.266g·cm^-3,μ（Mo Kα）=0.937mm^-1,F（000）=1112,R₁=0.0540,wR₂=0.1619。配合物（1）和（2）的中心锡原子均为畸变四面体构型。通过分子间氢键作用,配合物（1）形成二维网状结构。试验表明,配合物（1）和（2）具有良好的热稳定性,对人癌细胞Colo205、HepG2、MCF-7、Hela、NCI-H460增殖均有较强的抑制作用。     

DDQ/PPh3催化的N-苯甲酰苯胺衍生物中间体的有效合成及晶体结构

在DDQ/PPh₃作用下,以2-异丙基苯甲酸或水杨酸为原料,在温和条件下以较高的收率合成、分离得到两个化合物(2)和(3)。化合物(2)和(3)与苯胺在氯仿中加热回流可分别转化为酰胺类化合物(4)和(5)。所有化合物通过元素分析、质谱、核磁共振进行了表征,并解析了化合物(2)和(3)的X-衍射单晶结构。化合物1,2-二(2-异丙基苯甲酸)-2,3-二氰-5,6-二氯苯(2)晶体属单斜晶系,空间群P2₁/c,其晶胞参数为：a=1.2875(3)nm,b=1.5186(2)nm,c=1.5726(3)nm,β=122.23(3)°,V=2.6010(1)nm³,D_c=1.331g·cm^-3,Z=4,F(000)=1080,R₁=0.0572,wR₂=0.1260;化合物1,2-二(2-羟基苯甲酸)-2,3-二氰-5,6-二氯苯(3)晶体属三斜晶系,空间群P1,其晶胞参数为：a=0.87776(16)nm,b=1.13111(15)nm,c=1.18639(17)nm,α=69.290(2)°,β=89.409(3)°,γ=67.878(2)°,V=1.0104(3)nm³,D_c=1.542g·cm^-3,Z=2,F(000)=476,R₁=0.0383,wR₂=0.0931。强π-π堆积作用和分子间氢键将化合物(2)和(3)组装成稳定的三维结构。     

两个具stp三维拓扑构型的稀土配位聚合物{[Ln2（pda）3（H2O）2]2H2O}n（Ln=Nd/La）

本文利用水热合成方法,将稀土氧化物与邻苯二乙酸（H₂pda）反应得到了2个新颖的稀土配位聚合物{[Ln₂（pda）₃（H₂O）₂]·2H₂O}_n（Ln=Nd（1）,La（2））。测定了它们的晶体结构,并进行了X-射线单晶衍射、红外光谱、荧光光谱和热重分析等性质的表征。晶体结构测定表明这2个化合物为异质同晶化合物。属单斜晶系,C2/c空间群。晶体学参数分别为配合物1：a=2.62906（18）nm,b=1.61172（11）nm,c=0.78327（5）nm,β=93.173（5）°,V=3.3139（4）nm³,Z=4,F（000）=1840,μ=3.173mm^-1,D_c=1.878g·cm^-3,R₁=0.0226,wR₂=0.0609;配合物2：a=2.6271（14）nm,b=1.6149（8）nm,c=0.7966（4）nm,β=92.850（9）,V=3.375（3）nm³,Z=4,F（000）=1816,μ=2.570mm^-1,D_c=1.823g·cm^-3,R₁=0.0466,wR₂=0.1416。化合物中邻苯二乙酸配体连接相邻的稀土金属离子,形成复杂的具有stp拓朴构型的三维网络结构。     

基于2-(4-甲基苯甲酰基)苯甲酸及2，2'-联吡啶的双核铜(Ⅱ)配合物的晶体结构、荧光和磁性

以2-(4-甲基苯甲酰基)苯甲酸(HL)及2,2'-联吡啶(2,2'-bipy)为配体合成了一个双核铜(Ⅱ)配合物[Cu₂(L)₄(2,2'-bipy)₂]·H₂O(1),并对其进行了晶体结构测定。测定结果表明,该配合物晶体属于三斜晶系,空间群为P1,晶胞参数：a=1.01257(15)nm,b=1.3125(2)nm,c=1.3170(2)nm,α=82.985(2)°,β=76.437(2)°,γ=88.290(2)°,V=1.6887(4)nm³,D_c=1.391g·cm^-3,Z=2,F(000)=732,GooF=1.027,最终偏离因子R₁=0.0375,wR₂=0.0914。在配合物分子中相邻的2个铜(Ⅱ)离子通过2个2-(4-甲基苯甲酰基)苯甲酸根桥联配位连接起来,其端位各与1个2-(4-甲基苯甲酰基)苯甲酸根和1个2,2'-联吡啶分子配位,整个分子形成了双核结构。测定了标题配合物的荧光和磁性,结果表明：当激发波长为608nm时,配合物在472和476nm处有2个较强的荧光发射峰;在2~100K,配合物具有顺磁性。     

Nouvelle Synthese Des 2-Thioxoethylphosphonates, 2- mercaptovinylphosphonates, 2-Phosphoryl-3-thioxopropanoates, 2-Thiomethylvinylphosphonates, 2-Thioethoxycarbonylmethylvinylphosphonates

The cyanomethylphosphonates 1 and the ethyl phosphoacetates 2 were reacted with some fluorophenylisothiocyanates to give the 2-thioxoethylphosphonates 3 in tautomeric equilibrium with the corresponding 2-mercaptovinylphosphonates 3 ′ and the 2-phosphoryl-3-thioxopropanoates 4 , respectively. Reaction of the cyanomethylphosphonates 1 with fluorophenylisothiocyanates in presence of methyliodide furnished the 2- thiometylvinylphosphonates 5 . The 2-mercaptovinylphosphonates 3 ′ reacted with ethyl chloroacetate in refluxing ethanol in the presence of triethylamine to give S-substitued derivatives 6 .     

Reactions of 1,3-dioxacycloalkanes and their 2-arsena, 2-bora, 2-germa, 2-sila,and 2-thia analogs with nitriles

New reactions of five-, six-, and seven-membered 1,3-dioxacycloalkanes and their 2-arsena, 2-bora, 2-germa, 2-sila, and 2-thia analogs with nitriles giving rise to 1,3-oxazacycloalkanes and then to amino alcohols are surveyed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1499–1507, July, 2005.     

Crystal structures and hydrogen bonding schemes in four benzamide derivatives (2-hydroxy-benzamide, 2-hydroxy-thiobenzamide, 2-hydroxy-N,N-dimethyl-benzamide,and 2-Hydroxy-N,N-dimethyl-thiobenzamide)

Summary 2-Hydroxy-benzamide, C₇H₇NO₂; monoclinic; I2/a-C _2h ⁶ ;a=12.901 (2),b=4.982 (1),c=20.987 (3) Å; =91.50 (2)°;Z=8. 2-Hydroxy-thiobenzamide, C₇H₇NOS; monoclinic; P2₁/n-C _2h ⁵ ;a=13.508 (5),b=6.780 (2),c=15.878 (6) Å; =93.74 (5)°;Z=8. 2-Hydroxy-N,N-dimethyl-benzamide, C₉H₁₁NO₂; orthorhombic; Pbca-D _2h ¹⁵ ;a=11.752 (2),b=16.680 (3),c=9.079 (2) Å;Z=8. 2-Hydroxy-N,N-dimethyl-thiobenzamide, C₉H₁₁NOS; monoclinic; P2₁/c-C _2h ⁵ ;a=6.983 (1),b=11.652 (3),c=11.704 (3) Å; =100.02 (2)°;Z=4. The crystal structures of these four compounds were determined (respectively refined: 2-hydroxy-benzamide) by single crystal X-ray data. The refinements of the structure parameters by least squares methods yielded in all casesR<0.056. The hydrogen atoms were located by means of difference Fourier summations. The O-H ... O distances are 2.513 (1) Å in 2-hydroxy-benzamide (intramolecular) and 2.625 (1) Å in 2-hydroxy-N,N-dimethyl-benzamide (intermolecular). The two O-H ... S distances in 2-hydroxy-thiobenzamide are 2.904 (2) Å and 2.918 (2) Å (intramolecular, two molecules in the asymmetric unit) and 3.228 (2) Å in 2-hydroxy-N,N-dimethyl-thiobenzamide (intermolecular). Clear N-H ... O hydrogen bonds with 2.926 (1) Å and 3.006 (1) Å occur only in the structure of 2-hydroxy-benzamide (intermolecular).

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Die Kristallstrukturen und Wasserstoffbrücken-Bindungsschemata in vier Benzamid-Derivaten

Zusammenfassung 2-Hydroxy-benzamid, C₇H₇NO₂; monoklin; I2/a-C _2h ⁶ ;a=12.901 (2),b=4.982 (1),c=20.987 (3) Å; =91.50 (2)°;Z=8. 2-Hydroxy-thiobenzamid, C₇H₇NOS; monoklin; P2₁/n-C _2h ⁵ ;a=13.508 (5),b=6.780 (2),c=15.878 (6) Å; =93.74 (5)°;Z=8. 2-Hydroxy-N,N-dimethyl-benzamid, C₉H₁₁NO₂; orthorhombisch; Pbca-D _2h ¹⁵ ;a=11.752 (2),b=16.680 (3),c=9.079 (2) Å;Z=8. 2-Hydroxy-N,N-dimethyl-thiobenzamid, C₉H₁₁NOS; monoklin; P2₁/c-C _2h ⁵ ;a=6.983 (1),b=11.652 (3),c=11.704 (3) Å; =100.02 (2)°;Z=4. Die Kristallstrukturen dieser vier Verbindungen wurden mittels Röntgen-Einkristalldaten bestimmt (bzw. verfeinert: 2-Hydroxy-benzamid). Die Verfeinerungen der Strukturparameter nach der Methode der kleinsten Quadrate ergab in allen FällenR<0.056. Die Wasserstoffatome konnten anhand von Differenz-Fourier-Summationen belegt werden. Die O-H ... O-Abstände haben folgende Werte: 2.513(1)Å in 2-Hydroxy-benzamid (intramolekular) und 2.625(1) Å in 2-Hydroxy-N,N-dimethyl-benzamid (intermolekular). Die zwei O-H ... S-Abstände sind in 2-Hydroxy-thiobenzamid 2.904(2)Å und 2.918(2)Å (intramolekular, zwei moleküle in der asymmetrischen Einheit) und 3.228(2)Å in 2-Hydroxy-N,N-dimethyl-thiobenzamid(intermollekular). Klar zuzuordnende N-H ... O-Wasserstoffbrücken mit 2.926(1)Å und 3.006(1)Å treten lediglich in der Struktur des 2-Hydroxy-benzamid auf (intermolekular).

     

Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4)

Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4) (both argon and oxygen annealed samples) were calculated. The result indicated for both argon and oxygen annealed samples, Hg had the lowest valence for the highest Tc sample. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produce more carriers than argon annealed samples.     

离子色谱法测定尿液中的C2O42-、Ca2+、Mg2+

利用离子色谱法测定尿液中的草酸根、钙、镁离子：测定草酸根时，先在尿液中加入氯化钙使之转化成草酸钙沉淀，分离后用盐酸溶解草酸钙沉淀，然后进行测定测定钙、镁离子时，在酸性尿液中加入氧化剂过硫酸钾，在微沸状态下氧化尿液中的有机物，从而避免对色谱柱的污染：草酸根、钙、镁离子的回收率分别为108．3％～109．7％、94．9％～100．7％、97．2％～97.4％，相对标准偏差分别为2．4％、2.5％、3．1％。     

Reaction of 1, 1-Di-p-methoxyphenyl-2, 2-dinitroethylene and 1, 1-Di-O-methoxyphenyl-2, 2-dinitroethylene with 1-Benzyl-1, 4-dihydronicotinamide： Evidence for Concerted Electron-hydrogen Atom Transfer Mechanism

1,1-Di-p-methoxyphenyl-2, 2-dinitroethylene reacts with 1-benzyl-1, 4-dihydronicotinamide (BNAH) in deaerated acetonitrile to give 1,1-di-p-methoxyphenyl-2, 2-dinitroethane,while 1,1-di-O-methoxyphenyl-2, 2-dinitroethylene fails to react with BNAH under the same conditions, which provides evidence for a concerted electron-hydrogen atom transfer mechanism.     

2H-1, 2, 4-噻二唑并[2, 3-a]嘧啶衍生物的合成及除草活性测 定

合成了12种新的2-苯甲酰亚胺基-2H-1,2,4-噻二唑并[2,3-a]嘧啶类化合物,结构经IR,^1HNMR,MS和元素分析所确证,除草活性测定表明部分目标化合物具有较好的除草活性且选择性较好,对单子植物安全。     

DFT study and Monte Carlo simulation on proton transfers of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water

Density functional theory (DFT) and Monte Carlo (MC) simulation with free energy perturbation (FEP) techniques have been used to study the tautomeric proton transfer reaction of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water. Two reaction pathways were considered: the direct and water-assisted transfers. The optimized structures and thermodynamic properties of stationary points for the title reaction system in the gas phase were calculated at the B3LYP/6-311+G(d, p) level of theory. The potential energy profiles along the minimum energy path in the gas phase and in water were obtained. The study of the solvent effect of water on the proton transfer of 2-amino-2-oxozoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline indicates that water as a solvent is favorable for the water-assisted process and slows down the rate of the direct transfer pathway.     

Definitive heat of formation of methylenimine,CH2NH,and of methylenimmonium ion,CH2NH2+, by means of W2 theory

A long‐standing controversy concerning the heat of formation of methylenimine has been addressed by means of the W2 (Weizmann‐2) thermochemical approach. Our best calculated values, ΔH°_f,298(CH₂NH) = 21.1±0.5 kcal/mol and ΔH°_f,298(CH₂NH₂⁺) = 179.4±0.5 kcal/mol, are in good agreement with the most recent measurements but carry a much smaller uncertainty. As a byproduct, we obtain the first‐ever accurate anharmonic force field for methylenimine: upon consideration of the appropriate resonances, the experimental gas‐phase band origins are all reproduced to better than 10 cm^?1. Consideration of the difference between a fully anharmonic zero‐point vibrational energy and B3LYP/cc‐pVTZ harmonic frequencies scaled by 0.985 suggests that the calculation of anharmonic zero‐point vibrational energies can generally be dispensed with, even in benchmark work, for rigid molecules. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1297–1305, 2001     

Quantum-chemical Studies of Pyrimidin-4-ones. 2. Stability in the Gas Phase of Tautomers of Pyrimidin-2,4-dione, 2-Thioxo-, 2-Selenoxo-, 2-Amino-, and 2-Acetylaminopyrimidin-4-ones, and Their 6-Methyl- and 6-Phenyl Derivatives

The relative stability in the gas phase and the most probable reaction centers for electrophilic attack for the tautomers of pyrimidin-2,4-dione, 2-thioxo-, 2-selenoxo-, 2-amino-, and 2-acetylaminopyrimidin-4-ones, and their 6-methyl- and 6-phenyl derivatives have been investigated on the basis of the results of quantum-chemical calculations, using the semi-empirical PM3 method, without taking solvent effects into account.