Chem 261 1st Edition Lecture 10Outline of Last Lecture:I. Stereoisomers vs. Constitutional IsomersII. Ring Strain in CycloalkanesIII. Characteristics of Cyclic MoleculesOutline of Current Lecture:I. Cyclohexane Conformation continuedCyclohexane Conformations:To review…-Axial = up and down, Equatorial = sideways-Cis = same side, trans =opposite sidesNewman projection of cyclohexane:Cyclohexane: Chair conformation, strain free. Chair projection:-At room temperature, cyclohexane rings are conformationally mobile. Different chair conformations readily interconvert, exchanging axial and equatorial positions, called a “ring flip”. -In the above example, the newman projection of butane on the left is in gauche formation. On the right, after a ring flip, the molecule is in a more favorable formation. -Larger substituents prefer equatorial position-1 methyl group-> prefer equatorial position-Chair flips (w/ all hydrogens) are ALWAYS going on at room temperature. Freezing slows down chair flipsWhat happens when you have multiple substituents?-Bigger substituents = will dictate conformation and be in the equatorial position-Multiple substituents: 1-3, diaxial interaction-Torsion strain: avoid being gauche. Is the relationship between substituents on adjacent carbons.-Steric interactions: Between large substituents. 1-3, diaxial means the two carbons’ substituents with one carbon in
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