318-20 - CH 318 N LECTURE 20 Textbook Assignment Chapter...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
CH 318 N LECTURE 20 Textbook Assignment: Chapter 21 (Begin) Homework (for credit): POW 10 posted Today’s Topics: Conjugated Systems; Benzene and Aromaticity Notice & Announcements: Exam Papers: pick up @ Chem Office Organic Lecture Series 2 Conjugated Conjugated Systems Systems (Omit 20.3) (Omit 20.3)
Background image of page 1

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

View Full DocumentRight Arrow Icon
Organic Lecture Series 3 from heats of hydrogenation-relative stabilities of conjugated vs unconjugated dienes can be studied: Δ H 0 -237 (-56.5) 1,3-Butadiene -126 (-30.1) -127 (-30.3) kJ (kcal)/mol Name 1-Pentene 1-Butene trans- 1,3-Pentadiene 1,4-Pentadiene 2-Butene -115 (-27.6) cis- 2-Butene -120 (-28.6) -226 (-54.1) -254 (-60.8) Structural Formula Conjugated Conjugated Dienes Dienes conjugated Organic Lecture Series 4 conjugation of the double bonds in 1,3-butadiene gives an extra stability of approximately 17 kJ (4.1 kcal)/mol 2H 2 + catalyst Δ H 0 = 2(-127 kJ/mol) = -254 kJ/mol) 22 2 + Δ H 0 = -237 kJ/mol catalyst Conjugated Conjugated Dienes Dienes
Background image of page 2
Organic Lecture Series 5 Conjugated Conjugated Dienes Dienes C C C C H 2 C H C H C CH 2 The π systems of the 2 olefins overlap S-cis conformer Organic Lecture Series 6 C C C C H 2 C H C C H CH 2 S-Trans conformer Conjugated Conjugated Dienes Dienes
Background image of page 3

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

View Full DocumentRight Arrow Icon
Organic Lecture Series 7 – systems containing conjugated double bonds, not just those of dienes, are more stable than those containing unconjugated double bonds 3-Cyclohexenone (less stable) 2-Cyclohexenone (more stable) O O Conjugated Systems Conjugated Systems Most significant are α,β -unsaturated carbonyl Organic Lecture Series 8 O OH O Nu 1,2 Addition KineticProduct RLi and RMgBr 1,4 Addition Thermodynamic Product R 2 CuLi and RMgBr/Cu 1 2 3 4 1,2 1,2 vs vs 1,4 1,4 -Addition Addition
Background image of page 4
Organic Lecture Series 9 Simple Simple Rxn Rxn Coordinate Diagram Coordinate Diagram Δ H is (-) e.g. an Sn2 Mechanism Organic Lecture Series 10 A Two Step Mechanism: A Two Step Mechanism: Δ H is (-) e.g. an Sn1 Mechanism
Background image of page 5

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

View Full DocumentRight Arrow Icon
Organic Lecture Series 11 • Addition of 1 mol of HBr to butadiene at -78°C gives a mixture of two constitutional isomers: – these products can be explained by the following two-step mechanism 1-Bromo-2-butene 10% (1,4-addition) -78°C + + 3-Bromo-1-butene 90% (1,2-addition) CH 2 =CH-CH=CH 2 HBr 2 =CH-CH-CH 2 2 -CH=CH-CH 2 1,3-Butadiene H H Br 1,2 1,2 vs vs 1,4 1,4 -Addition Addition Organic Lecture Series 12 the key intermediate is a resonance-stabilized allylic carbocation: 1,2 1,2 - and 1,4 and 1,4 -Addition Addition 2 2 2 2 2 2 2 2
Background image of page 6
Organic Lecture Series 13 90% 10% 2 2 2 2 2 2 2 2 Organic Lecture Series 14 Kinetic Kinetic vs vs Thermodynamic Control Thermodynamic Control Δ G o = Δ H o –T Δ S o Gibbs Free energy Δ G = Δ H Δ S For transition states: 90% 10%
Background image of page 7

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

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/20/2009 for the course CH 318N taught by Professor Willson during the Spring '08 term at University of Texas.

Page1 / 19

318-20 - CH 318 N LECTURE 20 Textbook Assignment Chapter...

This preview shows document pages 1 - 8. Sign up to view the full document.

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