Chapter3notes.

Chapter3notes. - Lets Draw! Go to butane PES Draw Newman...

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1 Let’s Draw!! •Go to butane PES • Draw Newman projections of –Ec l ipsed •CH 3 /H eclipsed 3 /CH 3 eclipsed – Staggered butane •Gauche •Ant i Section 3.4 conformation of C 1 –C 2 3 4 & C 2 3 4 5 Conformations of higher alkanes 1 2 3 4 5 anti All bonds are ___________ ©Kay Sandberg
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2 Shapes of cycloalkanes Ideal bond angle for alkanes? H Bond angle in cyclopropane? Section 3.5 Angle strain: destabilization due to deviation from ideal angle values. Heat of combustion/methylene group cyclopropane: 697 kJ/mol Planar & bent bonds ©Kay Sandberg Shapes of cycloalkanes Ideal bond angle for alkanes? 109.5 o H Bond angle in cyclobutane? Section 3.5 ~90 o Heat of combustion/methylene group cyclopropane: 697 kJ/mol cyclobutane: 681 kJ/mol Dihedral angle: 20 o ©Kay Sandberg
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3 Shapes of cycloalkanes Ideal bond angle for alkanes? 109.5 o H H H H Bond angle in cyclopentane? Section 3.5 ~105 o Heat of combustion/methylene group cyclopropane: 697 kJ/mol cyclobutane: 681 kJ/mol cyclopentane: 658 kJ/mol Dihedral angle: 34 o ©Kay Sandberg Shapes of cycloalkanes Ideal bond angle for alkanes? 109.5 o Bond angle in cyclohexane? Section 3.5 ~111 o Heat of combustion/methylene group cyclopropane: 697 kJ/mol cyclobutane: 681 kJ/mol cyclopentane: 658 kJ/mol cyclohexane: 653 kJ/mol Dihedral angle: ~60 o ©Kay Sandberg
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4 Conformations of cyclohexane Chair conformation Section 3.6 H H H H H H H H H H H H H H H H H H H H CH 2 CH 2 All bonds are staggered •No torsional strain •No angle strain 1 6 2 5 3 4 foot rest arm rest head rest ©Kay Sandberg Conformations of cyclohexane Boat conformation Section 3.6 H C 1 H H H H H H H C 4 H C 6 H C 2 C 5 H C 3 H (H VDWradius 240 pm) •steric strain between flagpole H’s 180 pm Flagpole •torsional strain due to eclipsed bonds on 4 C ’s ©Kay Sandberg
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5 Conformations of cyclohexane Twist Boat conformation (skew boat) Section 3.6 H H H H H H H H H H •steric strain between flagpole H’s is reduced •torsional strain due to eclipsed bonds is ©Kay Sandberg Axial & equatorial bonds in cyclohexane Section 3.7 H H H H H H H H H H H H H H H H H H Axial H H H H H H H Equatorial H Chair conformation H H H H H H H H H H H H ©Kay Sandberg
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6 Section 3.7 1 6 2 5 3 4 1) On C-1 add a single bonded substituent in the axial position (label it X) 2) On C-6 add a single bonded substituent that is anti to X (label it Y) 3) On C-2 add a single bonded substituent that is gauche to X (label it Z)
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Chapter3notes. - Lets Draw! Go to butane PES Draw Newman...

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