Common Names of Alkyl Halides and Alcohols

Repulsion between the bonding electrons of one

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: repulsion between the bonding electrons of one substituent as they pass close to the bonding electrons of another substituent. Steric strain : results when atoms or groups are too close to each other. For C2-C3 rotation in butane: In the anti conformation the largest substituents are opposite each other most stable conformation. In the gauche conformations the largest substituents are adjacent to each other All eclipsed conformers have torsional and steric strain. In the Newman projection below, draw the most stable conformation of 1-chloro-4-methylpentane looking along C2-C3. You must draw the hydrogens on the Newan projection !
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34 Ring strain in cycloalkanes Cyclolkanes may twist and bend to minimize 3 different kinds of potential strain: 1. Angle Strain (deviation from 109.5° bond angle) 2. Torsional Strain (repulsion of the bonding electrons between nearby substituents) 3. Steric Strain (caused by atoms or groups of atoms approaching each other too closely) Conformations in cyclohexane Two main conformations: CHAIR and BOAT Both conformations are free of angle strain; however, the boat conformer has more torsional and steric strain than the chair. CHAIR BOAT Monosubstituted cyclohexanes Ring-flip : cyclohexane interconverts between two chair conformations (interconversion of axial and equatorial positions):
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35 Substituents in axial positions have 1,3-diaxial interactions (unfavorable steric interactions). Substituents in equatorial positions have fewer steric interactions (favorable). Disubstituted cyclohexanes Stereoisomers have different spatial orientations. Cis-trans stereoisomerism ( cis = same side, trans = opposite side)
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36 The conformer with the larger substituents in equatorial positions is the most stable.
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37 On the big chair below, draw the most stable conformation of cis-1-isopropyl-4-methylcyclohexane. Use the small chair as a guide to draw your bonds. Do not draw the hydrogens of the ring . Conformations of fused rings : cis and trans decalins:
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