Design, synthesis, and solid state NMR studies of molecular gyroscopes

Crystal engineering offers research opportunities at the interphase between organic and physical chemistry. Predicting crystal packing remains a major challenge in the field of crystal engineering, let alone incorporating function based on molecular motions. However, organic chemistry is a powerful ally in the study of the relationships between molecular structure, crystal packing, and function. This thesis comprises our studies in incorporating fast rotational dynamics in the solid state via the careful design and synthesis of rod-shaped organic compounds with rotary components. Our working molecular models are fashioned after macroscopic gyroscopes and compasses. The simplicity of gyroscopes consisting of a frame or stator, an axle, and a rotating mass, or rotator, makes them attractive synthetic targets. The gyroscopic frame in particular, possesses the additional critical function of protecting the rotator from steric contacts with adjacent molecular gyroscopes. This function is imperative in this work for the main goal of this thesis is to engineer free rotation in the solid state. The lead compounds presented in this thesis, 2c and 5, closely follow the structure of a simple gyroscope. They possess triptycyl and trityl groups that can act as stators, which we show in blue; ethylene axles shown in red; and a benzene ring, which can act as the rotator, also shown in red. An all enclosed molecular gyroscope has not been realized at the time this thesis is written.*; In Chapter 1 we present advances made in our research group toward the development of addressable molecular rotation in the solid state. The synthetic challenges in the synthesis of 2c are covered in chapter 2, where emphasis is placed in the Diels-Alder selectivity of benzyne with various substituted anthracenes.{09}It was found that benzyne can undergo 1,4- and 9,10- Diels-Alder cycloadditions with anthracenes that are alkyl-substituted at their 2, 3, 6, and 7 positions.; The solid-state rotational dynamics of 2c were studied using cross-polarization magic angle spinning and broad-line deuterium NMR techniques with static samples. The results of those studies are presented in chapter 3. A low activation energy of about 4.3 kcal/mole was estimated for the rotation of the benzene rotator for this compound.; The synthesis and solid-state rotational dynamics of an unsymmetrical molecular gyroscope, 1, are presented in chapter 4. This work is an exploration on the changes in physical properties brought upon by incorporation of stators with differing structures and physical properties. Molecular gyroscope 1 presents physical properties that show a compromise between those of triptycyl- and trityl-based gyroscopes. Like its symmetric counterparts, molecular gyroscope 1 suffers from interdigitation in the solid state at room temperature, precluding fast rotation of its phenylene rotator.; *Please refer to dissertation for diagrams.