chap4c - Sect 4.6 Monosubstituted cyclohexane rings...

Info iconThis preview shows pages 1–17. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Sect 4.6: Monosubstituted cyclohexane rings Methylcyclohexane conformations CH 3 CH 3 H H Equitorial methyl Axial methyl 1.7 kcal/mol 0 kcal/mol E E N N E E R R G G Y Y Energy difference between an axial and an equitorial methyl group CH 3 H CH 3 H H H CH 3 1,3-diaxial interactions 1,3-Diaxial interactions on the top of the ring STERIC REPULSION RAISES THE ENERGY OF THE AXIAL CONFORMATION H H H H H CH CH 3 H H H H H 1,3-diaxial interactions CH CH 1,3-Diaxial interactions: Newman projection view 1,3-Diaxial interactions 1,3-Diaxial interactions CH CH 3 CH CH 2 CH CH 2 gauche steric nteractions GAUCHE STERIC INTERACTIONS (like gauche butane) CH CH 3 CH CH 2 CH 2 Axial Equitorial No gauche steric problem when the group is equitorial Monosubstituted cyclohexanes: gauche steric interactions CH CH 3 CH CH 3 60 o 180 o Large groups will generally prefer to occupy an equatorial position where there is an absence of 1,3-diaxial (steric) interactions G Keep in mind, however, that the axial conformation will also be present, but in smaller amount. General rule General rule axial conformation equatorial conformation ∆ G o for group in the axial position CH - CH CH - CH -CH- CH CH -C- CH CH 1.7 1.8 2.1 >5 7.1 7.5 8.8 >21 Group X kcal/mol kJ/mol Group kcal/mol kJ/mol Cl- Br- HO- 0.4 0.5 0.7 C 6 H 5- 3.1 CH 3-C-O- O 0.7 1.7 2.1 2.9 13 2.9 Table 4.5: Conformational energy differences for substituents attached to a cyclohexane ring X X H H Equitorial preferred C C C C H H H H H H H H H t t-BUTYLCYCLOHEXANE-BUTYLCYCLOHEXANE Basically “locks” the ring in a chair with the tert-butyl group in the equatorial position. Too big a group to go into the axial position - must go equatorial. The axial value for this group in Table 4-5 ( >5 Kcal/mole) indicates a minimum value because there is so little axial that it is difficult to measure any real value. tert-Butylcyclohexane with the group axial HUGE steric strain Molecules viewed with Chime • Click on START, Click on PROGRAMS • Click on Netscape Communicator (4.7), then launch Netscape Navigator • Using Google, type in the address for the Dept. of Chemistry, WWU: http://www.chem.wwu • Select, course materials, select “WWU virtual molecular model set” • You may need the free program, Chime, to run this program. • Note: Internet Explorer and Netscape 7.1 won’t work! Sect 4.7: cis and trans isomerization in cycloalkanes cis-trans isomerism • Different spatial arrangements • The arrangements cannot be converted into one another by rotation • cis Both substituents on same side of plane • trans Substituents on opposite sides of plane cis cis and and trans trans isomers isomers cis trans applies to substituents on a ring or (later) double bond both substituents are on the same side of the ring the substituents are on opposite sides of the ring These two compounds are geometric isomers Cl Cl Cl Cl Cl Cl Cl Naming cis / trans isomers cis-1,2-dichlorocyclopropane trans-1,2-dichlorocyclopropane notice italics place designation in front of name Cl How many different dimethylcyclobutanes are there?How many different dimethylcyclobutanes are there?...
View Full Document

This note was uploaded on 09/17/2008 for the course CHEM 151L taught by Professor Roy,christopher during the Spring '08 term at Duke.

Page1 / 71

chap4c - Sect 4.6 Monosubstituted cyclohexane rings...

This preview shows document pages 1 - 17. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online