文本案例課件ch2upload-2cycloalkanes

1、Section 22013 Wei Dong Nanjing University of Science & Technology All Rights ReservedCycloalkanesChapter 2Simple CycloalkanesNaming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming

2、polycyclic compounds.3.2.13,3-dimethylbicyclo3.2.1octaneNaming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.tricyclo3.3.1.13,7decaneNaming polycyclic compou

3、nds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.Naming polycyclic compounds.bicyclo2.1.0pentane(Housane)Naming polycyclic compounds.Ring StrainIn cycloalkanes, steric interactions are important indetermining ground-state stability a

4、nd conformation.For example, in cyclopropane, ring hydrogens are forcedinto an all-eclipsed conformation. This eclipsing generatesapproximately 6 kcal/mole of torsional strain energy.Ring strain as a result ofinterorbital angles of 104,with poor orbital overlap.In addition to torsional strain, ring

5、strain destabilizecyclopropanes by about 25 kcal/mole.Heat of Combustion/CH2 for Cycloalkanes, showing theeffect of Ring StrainIn cyclobutane, the ring “puckers” to relieve eclipsinginteractions, but the bond angles are still strained at 90o.This type of puckering is also evident in cyclopentane, wh

6、erethe interior bond angles are strained at 120o.In cyclohexane, all bond angles are 109o and all hydrogensare anti- to each other, making strain energy very small.In cyclohexane, two distinct types of hydrogens are evident;one set which are perpendicular to the ring plane andanother which are “with

7、in” the ring plane.In cyclohexane, two distinct types of hydrogens are evident;one set which are perpendicular to the ring plane andanother which are “within” the ring plane.The effect of ring inversion is that all axial substituents e equatorial, and all equatorial substituents e axial.these forms

8、will not be equal in energy, however, because ofaxial hydrogen-methyl interactions, and the conformer withthe equatorial methyl will predominate at equilibrium.This effect is most evident when large atoms or large side-chainsare attached to the ring. For example, in bromocyclohexane, theequilibrium

9、strongly favors the isomer with the bromine in theequatorial position.Axial alkyl groups also sterically interact with axial hydrogens,strongly favoring the conformer with the alkyl group in theequatorial position.Movie clip showing alkyl-hydrogeninteractions in the axial conformer.In tert-butylcycl

10、ohexane, this effect is so significant that thering is essentially “frozen” with the tert-butyl groupequatorial.cis- trans- Isomerism in disubstituted cycloalkanesIn cyclopropane, two isomers are possible.In cyclobutane, two 1,2-substituted isomers are possible.along with two 1,3-substituted isomers

11、.1,2-a-e = cis1,2-e-e = trans1,3-e-e = cis1,4-a-e = cis1,3-a-e = trans1,4-e-e = transDraw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:Draw the following compound in its

12、most stable conformation:Draw the following compound in its most stable conformation:But this chair has twoaxial chlorines!Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformati

13、on:Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:Draw the following compound in its most stable conformation:But this structure has two axialsubstituents, therefore w

14、e will redraw itin the most stable chair conformation.But this structure has two axialsubstituents, therefore we will redraw itin the most stable chair conformation.But this structure has two axialsubstituents, therefore we will redraw itin the most stable chair conformation.Draw the following compounds in their most stableconformation:Draw the following compounds in their most stableconformation:Draw the follow