Daniel MaurerFollow

Date of Award

2016

Document Type

Honors Thesis (Open Access)

Department

Colby College. Chemistry Dept.

Advisor(s)

Dasan M. Thamattoor

Second Advisor

Nicholas Boekelheide

Abstract

Part I

Photolysis of phenanthrene-based methylenecyclopropane derivatives have previously been shown to generate alkylidenecarbenes, which readily rearrange to form alkynes. In this work, we show that photolysis of an analogous cyclic alkylidenecarbene precursor at ambi- ent temperature forms cyclohexyne via the putative cyclopentylidenecarbene, and can be trapped by dienes via a Diels-Alder reaction. Cyclohexyne and other strained cycloalkynes are of much interest to theoreticians and experimentalists alike. Results of coupled-cluster and DFT calculations on the potential energy surface of cyclopentylidenecarbene and the corresponding strained cyclohexyne are also presented. The photochemical generation of cy- clopentylidenecarbene, and thus cyclohexyne, from a hydrocarbon precursor that is readily synthesized and conveniently handled is a first, and will likely facilitate further structural studies using matrix isolation spectroscopy and kinetic investigations by ultrafast laser flash photolysis.

Part II

Aromaticity, a term still debated to this day, is a fundamental concept for chemists. Also under scrutiny is the idea that aromatic ring currents explain the diamagnetic anisotropic properties of aromatic compounds. Systematic approaches to evaluate the effect of magnetic shielding from aromatic ring currents have mainly focused on varying a substituent on an aro- matic ring. This work synthesized bistriptycenyltoluene in order to study the through-space shielding effect. The synthetic method used is applicable to study the through-space shield- ing effect on a variety of substituents. In bistriptycenyl derivatives, the substituent is in the shielding region of four benzene rings (red) and the deshielding region of three benzene rings (blue). Furthermore, experimental chemical shifts are compared to computational findings based on the quantum mechanical procedures suggested by Rablen and Bally. Interestingly, the bistriptycenyltoluene also has the potential to demonstrate molecular gearing motions, and the synthetic route presented here can be used to prepare other molecular gears.

Keywords

carbene, photolysis, cyclohexyne, strained molecules, triptycene, aromaticity

Download

Share

COinS