Methyl and T-Butyl Group Reorientation in Planar Aromatic Solids: Low-Frequency Nuclear Magnetic Resonance Relaxometry and X-Ray Diffraction

We have synthesized 3-t-butylchrysene and measured the Larmor frequency omega/2pi (= 8.50, 22.5, and 53.0 MHz) and temperature T (110-310 K) dependence of the proton spin-lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-butylchrysene using x-ray diffraction, which indicates the presence of a unique t-butyl group environment. The spin-1/2 protons relax as a result of the spin-spin dipolar interactions being modulated by the superimposed reorientation of the t-butyl groups and their constituent methyl groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in-plane methyl group and the entire t-butyl group reorient with a barrier of 24.2 +/- 0.9 kJ mol(-1), and the two out-of-plane methyl groups reorient with a barrier of 14.2 +/- 0.6 kJ mol(-1). Following a brief review of methyl group rotation in simple ethyl-, and isopropyl-substituted one- and two-ring aromatic van der Waals molecular solids, the barriers for the out-of-plane methyl groups and the t-butyl group in 3-t-butylchrysene are compared with those barriers in three related molecular solids whose crystal structure is known: 4-methyl-2,6-di-t-butylphenol, 1,4-di-t-butylbenzene, and polymorph A of 2,6-di-t-butyl- naphthalene. A trend is observed in the reorientational barriers for the t-butyl and the out-of-plane methyl groups across this series of four compounds: as the t-butyl barriers decrease, the out-of-plane methyl barriers increase

Placing the library at the heart of plagiarism prevention: The University of Bradford experience.

yesPlagiarism is a vexed issue for Higher Education, affecting student transition, retention and attainment. This paper reports on two initiatives from the University of Bradford library aimed at reducing student plagiarism. The first initiative is an intensive course for students who have contravened plagiarism regulations. The second course introduces new students to the concepts surrounding plagiarism with the aim to prevent plagiarism breaches. Since the Plagiarism Avoidance for New Students course was introduced there has been a significant drop in students referred to the disciplinary programme. This paper discusses the background to both courses and the challenges of implementation

Should clauses prohibiting assignment be overridden by statute?

Many contracts for the supply of goods or services include a clause prohibiting assignment by the supplier of its rights under the contract. The existence of such clauses, both in particular contracts and more generally, can have a chilling effect on the use of receivables as collateral to obtain financing. Thus, in many jurisdictions, there is a legislative override for such clauses, so that they are not enforceable against third parties. There is an ongoing debate as to whether English law should follow suit and, if so, what form the override should take, which has now led to a power to make reforms being included in sections 1 and 2 of the Small Business, Enterprise and Employment Act 2015. This chapter examines the arguments for and against an override in English law, informed by two small-scale surveys undertaken by the author and others over the last four years. Many contracts for the supply of goods or services include a clause prohibiting assignment by the supplier of its rights under the contract. The existence of such clauses, both in particular contracts and more generally, can have a chilling effect on the use of receivables as collateral to obtain financing. Thus, in many jurisdictions, there is a legislative override for such clauses, so that they are not enforceable against third parties. There is an ongoing debate as to whether English law should follow suit and, if so, what form the override should take, which has now led to a power to make reforms being included in sections 1 and 2 of the Small Business, Enterprise and Employment Act 2015. This chapter examines the arguments for and against an override in English law, informed by two small-scale surveys undertaken by the author and others over the last four years.</p

‘Sales’ on Retention of Title terms: is the English law analysis broken?

Hard cases make bad law. The history of the Bunkers litigation in the English courts demonstrates, as is often the case, that the history and context of litigation can have a strong and decisive effect on both the result and the legal reasoning leading to that result. This article argues that, while the decision of the Supreme Court in the Bunkers case was understandable given its context and background, it, together with the decision of the Court of Appeal in Caterpillar v Holt, has led to such uncertainty surrounding the use of retention of title (‘ROT’) clauses in inventory financing, that it is time for a reanalysis of the legal position. This article sets out suggested options for that reanalysis, some more radical than others

‘Sales’ on Retention of Title terms: is the English law analysis broken?

Hard cases make bad law. The history of the Bunkers litigation in the English courts demonstrates, as is often the case, that the history and context of litigation can have a strong and decisive effect on both the result and the legal reasoning leading to that result. This article argues that, while the decision of the Supreme Court in the Bunkers case was understandable given its context and background, it, together with the decision of the Court of Appeal in Caterpillar v Holt, has led to such uncertainty surrounding the use of retention of title (‘ROT’) clauses in inventory financing, that it is time for a reanalysis of the legal position. This article sets out suggested options for that reanalysis, some more radical than others