Conformational Properties of 2-Halocyclohexanones

Background

Your experimental group conducts research in organic chemistry at the University of Massachusetts at Amherst. Recently, you came across an article in the Journal of Chemical Research [J. Chem. Res. 1 1257-59 (1997)] which gave some interesting results. The title and abstract from the paper are reprinted here.

The Infrared Spectra of a-Brominated Ketosteroids

Newton, U.R. and Crane, I.M.

Chemistry Dept., University of Massachusetts at Amherst, MA. USA

Through a study of various ketosteroids we have determined that the introduction of an a-bromo substituent shifts the carbonyl (ketone) stretching frequency +13 to 25 cm-1 if the carbon-bromine and carbon-oxygen bonds are approximately in the same plane, but has relatively little effect if the C-Br and C-O bonds are far from coplanar.

 

You believe your research group has the necessary skills and equipment to investigate the results of Newton and Crane. In particular, you'd like to determine why these two "classes" of compounds might give such different spectral results. Since you are more interested in the effect noted by Newton than in the specific chemistry of ketosteroids, you will use simpler, model compounds in your experiment for which syntheses are readily found. After synthesizing cyclohexanone and 2-bromocyclohexanone, you will use FT-IR spectroscopy and molecular modeling to explore Newton's observations. Additionally, your group will consider spectroscopic and modeling results for 2-chlorocyclohexanone to see if further trends among this series of compounds can be discovered.

Your Objective

Your group will need to make cyclohexanone and 2-bromocyclohexanone (2-chlorocyclohexanone will be purchased since a suitable synthesis has not been found). Individually, each of you will need to develop a thorough pre-lab procedure for one of the above compounds, based on the relevant journal article footnoted below. In addition to writing out in detail all stages of the experiment, be sure to include equipment and glassware you plan to use and sketches of your apparatus where necessary. You should scale the reaction to give a reasonable amount of product for all subsequent analysis (0.5 - 1 mL is plenty for GC and FT-IR). You will have one week to complete and submit the pre-lab procedure and then a second week to make any necessary revisions (see Experiment Schedule).

The syntheses will be done during the first week of the experiment. It is to your advantage to complete all synthetic work during this first week since some of the compounds may degrade with air and/or light exposure. For the same reason it is a good idea to do GC and FT-IR work as soon as possible. If a second week is necessary to complete your synthetic or analytical work, store your reaction mixture or compound in a sealed container in the lab refrigerator.

The remaining two weeks of the experiment will involve finishing up synthetic work in lab, 2 hours of FT-IR work outside of lab (scheduled with Deb), modeling your compound using Spartan on your own time, and a 1-2 hr discussion meeting held the final week of the experiment during regularly scheduled lab time. To this meeting, be sure to bring all your original data, a write-up of your group's experimental findings ("Data" section), and a first draft of your "Discussion" section in which you speculate on what your group's data reveals about the conformational properties of the compounds you have studied. You should get together with your research group prior to this meeting in order to exchange data and discuss any trends that you observe in this series of compounds. Each person is responsible for handing in their own Data write-up (of the group's findings) and a rough draft of a Discussion section at our discussion meeting. At this meeting, we'll review your observations and speculations, and talk about guidelines for writing up a comprehensive report of your results. Reports may be submitted individually or as a group.

2 Calo, V., Synthesis 1978, 139-40.