Carbonylcyclohexanone Lab Report

Experiment 7A: Carbonyl Reduction: Sodium Borohydride Reduction of 4-tert-Butylcyclohexanone

Experiment 7A, Carbonyl Reduction: Sodium Borohydride Reduction of 4-tert-Butylcyclohexanone, provides firsthand experience with carbonyl reductions. NaBH4, a mild reducing agent, was used to reduce the ketone functional group in the compound, 4-tert-Butylcyclohexanone, that was then protonated using hydrochloric acid to produce two diastereomers (cis/trans) of 4-tertbutylcyclohexanol. Moreover, this experiment refined skills in using H-NMRs (integration, multiplicity, and coupling constants) to effectively distinguish between cis and trans isomers of a desired product. To begin the experiment, 50 mg of 4-t-butylcyclohexanone and methanol were added to a conical vial. NaBH4 was then added to the reaction mixture to reduce the ketone functional group (present in the starting material). The reaction was allowed to proceed for 30 minutes and was subsequently quenched using hydrochloric acid. The addition of hydrochloric acid permitted the protonation of the reduced ketone (O-) to form the two diastereomer

Cis-isomers have a dihedral angle of 90˚ resulting in a relatively low coupling constant and low splitting. Trans-isomers have a dihedral angle of 180˚ producing a relatively high coupling constant indicating increased splitting. Thus, the two compounds were also distinguished based on the observed splitting of the two peaks. With respect to a Newman projection for the C1-C2 bond of each product, the relative splitting was determined. For the trans-product the Newman projection exhibited a dihedral angle of 60˚ between H1 and H2, while H1 and H2’ exhibited a dihedral angle of 180˚. The H1 single was therefore split into a triplet of triplets by two different groups of hydrogens. https://www.odinity.com/hydride-reduction-reactions-stereoselective-adventure/ Trans C1-C2 Trans