Fitzgerald L J, Gerkin R E
Department of Chemistry, Ohio State University, Columbus 43210.
Acta Crystallogr C. 1993 Nov 15;49 ( Pt 11):1952-8. doi: 10.1107/s0108270193002641.
The structures of 1-naphthoic acid and 2-naphthoic acid have been investigated in order to determine the degree of disorder of the carboxylic acid groups. 1-Naphthoic acid was found to be completely ordered with C--O bond lengths of 1.214 (3) and 1.312 (3) A, and C--C--O bond angles of 124.8 (2) and 114.2 (2) degrees. 2-Naphthoic acid was found to possess a significant degree of disorder with C--O bond lengths of 1.256 (3) and 1.274 (3) A, and C--C--O bond angles of 117.7 (2) and 119.1 (2) degrees. In 2-naphthoic acid, the acid H atom was refined at two sites with 0.5 occupancy at each. Analysis of the anisotropic displacement ellipsoids of the acid O atoms for each structure demonstrated that these parameters are consistent with thermal motion of the O atoms. These results indicated that the proton, but not the O atoms, is disordered in the carboxylic acid group of 2-naphthoic acid. In each structure, the acid molecules form cyclic dimers about inversion centers, with an O...O(acceptor) distance of 2.653 (3) in 1-naphthoic acid and 2.618 (3) A in 2-naphthoic acid. The cyclic dimers form layers in each of these structures wherein lateral closest intermolecular approaches to the acid O atoms are from ring H atoms. The intermolecular O...H close approaches, together with the intramolecular close approaches, are very uniform in distance and angle of approach for the two O atoms in the 2-naphthoic acid structure.(ABSTRACT TRUNCATED AT 250 WORDS)
为了确定羧酸基团的无序程度，对1-萘甲酸和2-萘甲酸的结构进行了研究。发现1-萘甲酸完全有序，其C—O键长为1.214(3)和1.312(3)Å，C—C—O键角为124.8(2)和114.2(2)度。发现2-萘甲酸具有显著程度的无序，其C—O键长为1.256(3)和1.274(3)Å，C—C—O键角为117.7(2)和119.1(2)度。在2-萘甲酸中，酸H原子在两个位置进行精修，每个位置占有率为0.5。对每种结构的酸O原子的各向异性位移椭球分析表明，这些参数与O原子的热运动一致。这些结果表明，在2-萘甲酸的羧酸基团中，质子是无序的，而O原子不是。在每种结构中，酸分子围绕反演中心形成环状二聚体，1-萘甲酸中O…O(受体)距离为2.653(3)，2-萘甲酸中为2.618(3)Å。这些结构中环状二聚体形成层，其中酸O原子横向最接近的分子间接近来自环H原子。对于2-萘甲酸结构中的两个O原子，分子间O…H近距离接近以及分子内近距离接近在距离和接近角度上非常均匀。(摘要截短于250字)
