School of Natural and Environmental Sciences

Event items

Distortions, deviations, and alternative facts: reliability in crystallography

Chemistry Seminar Series - Emeritus Professor Bill Clegg, Newcastle University

Date/Time: Tuesday 12 February 2019, 14:00 - 15:00

Venue: Room 2.76, Bedson Building

Abstract

This seminar is a modified version of my invited plenary Lonsdale Lecture given at the 2018 British Crystallographic Association annual meeting.

The Lonsdale Lecture is intended to serve an educational purpose as well as reporting research results, with the lecturer each year being nominated by the BCA Young Crystallographers’ Group. 

One of the research results for which Kathleen Lonsdale is best known was her 1929 demonstration that the benzene ring in crystalline hexamethylbenzene is planar and has essentially hexagonal symmetry, resolving decades of dispute among organic chemists.

More recent crystallographic studies of hexamethylbenzene have shown that there are actually small deviations from planarity.

Such deviations for aromatic compounds may be due to electronic, steric, and/or intermolecular factors.

Some substituted benzene molecules display remarkably large deviations, both from a planar ring structure and from regular hexagonal angular geometry around the ring.  I have encountered both kinds of distortion during my research career.

Starting from this specific connection with Kathleen Lonsdale’s research, my lecture will recount a number of stories of structural distortions and deviations from expected results and explanations that have been suggested for them, across a wide range of chemical topics.

On the way we will find genuine surprises and results that have led to new understanding, but also examples of poor experiments, misinterpretation of data, scientific bias and preconceived ideas, incompetence, and even deliberate fraud.

While showcasing some interesting research in its own right, this will give useful information on the interpretation of the limitations, capabilities, and results of X-ray crystallography as applied in chemistry and, I hope, also provide some entertainment!