The crystal structure of the monoclinic form of n‐hexatriacontant
The crystal structure of the monoclinic form of n‐hexatriacontant
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单斜晶型正三十六烷的晶体结构
DOI：
10.1107/s0365110x5600111x
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发表时间：
1956
期刊：
影响因子：
--
通讯作者：
V. Vand
中科院分区：
文献类型：
--
作者：
H. Shearer;V. Vand
通过 X 射线测定了正十六烷单斜晶形式 C3eH74 的晶胞。它是a----5.57，b----7.42，c--48.35 _~，fl----119 6'，每个细胞有两个分子，空间群为C~ h-P21/a。借助子晶胞理论准备了傅立叶投影并确定了原子坐标。这些链基本上堆积在具有 a0-~ 4-945、b0--7.42、co----2.546~、空间群 D~-Pbnm 的正交子晶胞中，但结构因子计算需要单斜晶子晶胞。该链在实验误差范围内是规则的和周期性的，平均单CC键长为1.534±0.006/~，锯齿形键角为112 1'±21'。引言准确测定正构烷烃晶体结构的兴趣有两个方面：环境对碳键长和角度的影响值得研究，多晶型的细节需要阐明。 Smith (1953) 最近取得了相当大的进展，他表明 Mfiller (1928) 描述的奇斜方碳氢化合物的空间群是 D~-Pbcm，而不是 le Dg~-Pnam。 Smith 还表明，即使是正交菱形碳氢化合物，(00l) 长间距也减半，Bunn（私人通讯）也证实了这一点，因此 Vand (1953) 从粉末数据获得的正交菱形 n-CaeHTa 的 c 轴需要加倍。 Smith还发现，nC~8以上的纯偶烷烃在室温下通常会结晶为单斜晶系，而邻近同系物中约2%的杂质会将它们转变为斜方晶系形式，杂质的量随着链长的增加而减少。由于我们的单斜晶体是通过对 Vand (1953) 用于密度测定的斜方材料进行重结晶而获得的，因此可以从 Smith 的数据推断，在重结晶过程中发生了一些纯化，并且原始斜方材料的纯度可能低于约 98-99%，而本工作中使用的单斜晶体具有更高的纯度。然而，由于实验困难，事实证明不可能在质谱仪中检查这一点。
The unit cell of the monoclinie form of n-hexatriacontane, C3eH74, was determined by X-rays. It is a----5.57, b----7.42, c--48.35 _~, fl----119 6', with two molecules per cell and space group C~ h-P21/a. Fourier projections were prepared and atomic co-ordinates determined with the aid of the subcell theory. The chains pack essentially in an orthorhombic subcell with a0-~ 4-945, b0--7.42, co----2.546~, space group D~-Pbnm, but a monoclinic subcell is needed for structure-factor compu-tations. The chain is regular and periodic within experimental error, with an average single CC bond length 1.534±0.006/~ and the zigzag bond angle 112 1'±21'.Introduction The interest in accurate crystal-structure determina-tion of n-paraffins is twofold: the effect of environ-ment on the bond lengths and angles of carbon de-serves study and the details of polymorphism need elucidation. Considerable advance has recently been made by Smith (1953), who showed that the space group of the odd orthorhombic hydrocarbons de-scribed by Mfiller (1928) is D~-Pbcm instead of le Dg~-Pnam. Smith has also shown that for even ortho-rhombic hydrocarbons the (00l) long spacings are halved, a point also confirmed by Bunn (private communication), so that the c axis of the ortho-rhombic n-CaeHTa, obtained by Vand (1953) from powder data, needs to be doubled. Smith also found that pure even paraffins above nC~ 8 normally crys-tallize as monoclinic at room temperature, whereas about 2% impurity of neighbouring homologues changes them to the orthorhombic form, the amount of impurity decreasing with increasing chain length. As our monoclinic crystals were obtained by recrystal-lization of the orthorhombic material used by Vand (1953) for density determination, one can infer from Smith's data that during recrystallization some purif-ication took place and that the original orthorhombic material was probably less than about 98-99% pure, whereas the monoclinic crystals used in the present work were of a higher purity. However, it proved im-possible to check this in a mass spectrograph owing to the experimental difficulties.