Week 6 Chem 333
Week 6 Chem 333 CHEM 333 001
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This 9 page Class Notes was uploaded by Hayley on Sunday October 4, 2015. The Class Notes belongs to CHEM 333 001 at University of South Carolina taught by John Lavigne in Summer 2015. Since its upload, it has received 40 views. For similar materials see Organic Chemistry I in Chemistry at University of South Carolina.
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Date Created: 10/04/15
Continue Conformations 9 Newman projections Conformations Molecules can be exible They can bend twist etc Predicting how molecules bend twist etc in space Can be in or positions Why is it important Certain reactions can only take place during a certain conformation Two types of drawings 0 Newman Projections 0 Chair Newman Projections Need to know 0 O O O Wedge 9coming towards you Dash 9Going away from you Used to clearly see both groups from a 3D perspective Looking down a carboncarbon bond and 3 groups attached to each carbon How to read this Newman projection O 0000 g 5 E f a front carbon b back carbon Me methyl group Central point Cl F and Me 9 1st carbon Circle back carbon and it s elements J 339 Fl 1 L 39 a quot x K l quot 3 fixquot J l ygk x r i All i j Fix g 1 Groups can be 0 Staggered 9 can see all groups 1 o Eclipsed 9 can t see back groups Acyclic alkanes Example Butane 9 C4H10 9 looking down C2C3 bond jfi a f H i w quoti In terms of Energy does A C No They are both staggered but aren t the same energy Therefore B D even though both are eclipsed A vs C 9 C is higher in energy than A B vs D 9 D is higher in energy because CH3 is together is always has a lower energy than Staggered favored position most stable Eclipse non favored position least stable Energy D B C A Know from newton projection above A antiperiplanar conformation B anticlinal conformation Other C gauche D synperiplanar Cyclic Alkanes C3 Cyclopropane Always eclipsed 0 Has a high torsional strain Always in same plane Angle strain deviation from preferred bond angle 0 Bond angle CCC I Want 1095 I Have 60 The sigma bonds in Cyclopropane are bent and have a weird overlap They are referred to as banana bonds 0 In terms of reactivity these bonds are more reactive less stable than normal sigma bonds C4 Bond angle 0 Want 1095 Have 90 Twist it and it reduces torsional strain but increases angle strain Eclipsed OOOO Butter y conformation redLLC s lnCrrcuseS 4 hm stoned mam Sim n 8 am C5 Cyclopentane Bond angle 0 Have 180 0 Want 1095 Those degrees are close together small angle strain 0 Eclipsed Has a high torsional strain atplanar because everything is eclipsed but twisting will reduce it Envelope conformation C6 Cyclohexane staggered Bond angle 0 Have 120 0 Want 1095 Chair conformation q 4 if i 3 l i T r f J E i F i 7 f 3 M W i if PL 6 fut L B f z J i l Acyclic energy vs Cyclic energy Higher energy cyclic AAG z 28 kcalmol in Xi L l T 5K up I I a I if X I 9 f Chair Conformation continue C6 A lot of exibility stability Axial Equatorial Bond angle 110 Substituents don t want to be axial During a chair ip axial becomes equatorial equatorial becomes axial These are not the same energy If you put anything bigger than hydrogen in axial position it will increase the energy of that conformation vertical up down axial horizontal across equatorial a l 3 m I a M x W i 39R 7 a f are a a gemJ 9 a Chocx i yZ ChatIf 509le y Chair girl s Ch I 12 chair is higher in energy bc of 5 carbons in same area sterics chairmost stable substituents will in uence stability 9 when electrons are closer in space More electron density put with small amount of electron densitytorsional strain across ring A and B SameCis C and D DifferentTrans AW 4 A my 9 g 7 r 7 H
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