Structure in Chemistry
CA14. Solutions to selected problems
With contributions from Dr. Edward McIntee, CSB/SJU
a) The substituents are always trans along the junctions between each pair of rings. The steroids resemble a series of trans-decalin structures.
b) The overall structure would be more wide and wavy like a trans-decalin, rather than curled or boxy like a cis-decalin.
a) Bicyclo[2.1.1]hexane b) Bicyclo[3.2.1]octane c) Bicyclo[2.1.0]pentane (more commonly called "housane")
d) Bicyclo[2.2.2]octane e) cis-Bicyclo[3.3.0]octane
f) cis-Bicyclo[1.1.0]butane g) Bicyclo[1.1.1]pentane h) Bicyclo[4.3.3]dodecane
Although we could sketch out many rings using adamantane, just three rings are needed to include all the carbon atoms in the structure. Thus, adamantane is considered a tricyclic system. The systematic nomenclature of tricyclic systems gets a little more complicated, so we won't worry about that.
If cyclodecane adopted a regular diamond lattice conformation, there would be a whopping 8 atom interaction in the middle of the ring. That interaction isn't even included in our basis set. It would cost at least 6-7 kcal/mol. As a result, the cyclodecane adopts a twisted structure to avoid this interaction.
a) The β-D-glucose isomer should be the more stable isomer. The β-D-glucose
isomer places the C1 hydroxyl group in the equatorial position.
b) The β-D-glucose isomer should be the more abundant isomer.
c) This is due to something called the anomeric effect. In solvents of modest polarity, such as dicholoromethane, the α-D-glucose isomer is not as polar as the β-D-glucose isomer. In the α-D-glucose isomer the dipoles of the ring oxygen and the C1 hydroxyl group opposing each other (therefore the overall effect is the molecule is less polar). In addition, the α-D-glucose isomer is stabilized by hyper conjugation of the ring oxygen and C1. For more information see http://en.wikipedia.org/wiki/Anomeric_effect
d) A more polar environment would promote having more of the β-D-glucose isomer around. In the β-D-glucose isomer, the dipoles of the ring oxygen and the C1 hydroxyl group align each other (therefore the overall effect is the molecule is more polar).
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Structure & Reactivity in Organic, Biological and Inorganic Chemistry by Chris Schaller is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.
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