1_Delocalized_System

1_Delocalized_System - CHEM 267 Basic Organic Chemistry 2...

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Prof. Dr. Xiangdong Fang University of Waterloo CHEM 267 Basic Organic Chemistry 2 1
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Chem 267 Basic Organic Chemistry 2 Text: Organic Chemistry, Structures and Functions, Volhardt and Schore, 5 th Ed., W. H. Freeman and Company© 2007 (with study guide) Quizzes: Chemportal. Every two weeks. Method One of Evaluation Quizzes 5% Midterm Test (50 minutes in class) Thursday, March 3rd 30% Final Exam: (held during the normal exam period) 65% Method Two of Evaluation Midterm Test (50 minutes) Thursday, March 3rd 30% Final Exam: (held during the normal exam period) 70% Method Three of Evaluation Final Exam: (held during the normal exam period) (not recommended) 100% i-Clickers are not going to be used in Section one of CHEM 267. Class participation is not required, but is strongly suggested that students should attend all classes of the course. 2
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Chem 266 Reviews Valence Electrons , 8-Electron Rule , Formal Charge Lone Pair of Electrons N formal charge at the nitrogen ? A) neutral; B) positive; C) negative; O number of lone pairs at the oxygen ? A) 1; B) 2; C) 3; D) 0; formal charge at the carbon ? A) neutral; B) positive; C) negative; C H 3 C CH 3 CH 3 3
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Chem 266 Reviews π -Conjugation , Resonance Structures 4 O O O O O O 6-electron oxygen is worse! 6-electron carbon is OK! O O O O Pay Attention to the 8-Electron Rule and Electronegativity for Each Atom H 3 C
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5 Chem 266 Reviews VSEPR (Valence Shell Electron-Pair Repulsion) Theory C H H H H Tetrahedral N H H H O H H Trigonal pyramidal Bent 109.5 ° 107 ° 105 ° CC H H H H B F F F Trigonal planar 120 ° CN H H H CO H H Be H H HH H H Linear 180 ° +
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6 Chem 266 Reviews VB (Valence Bond) Theory
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7 Chem 266 Reviews Orbital Hybridization Experimental Result VSEPR VB Be Cl Cl 180 o Linear identical Be-Cl bond Be Cl Cl 180 o , minimum repulsion Linear 1s 2 2s 2 2p 0 energy Be atom 1s 2 2s 1 2p 1 But 2s and 2p orbitals are different! Orbital Hybridization (2s and 2p energy levels are very close) energy 1s 2 2s 1 2p 1 2sp 2p 1s 2 2x sp hybridized orbitals are equal! sp Hybridization : BeCl 2 Molecule
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8 Chem 266 Reviews H H C C C + C p p sp sp sp sp p p Experimental Result VB H 180 o Linear 1s 2 2s 2 2p 2 energy Ca tom 1s 2 2s 1 2p 3 But 2s and 2p orbitals are different! Orbital Hybridization (2s and 2p energy levels are very close) energy 1s 2 2s 1 2p 3 2sp 2p 1s 2 2x sp hybridized orbitals are equal! H form 2x bonds form 2x bonds sp Hybridization : Acetylene Molecule
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9 Chem 266 Reviews Trigonal planar C R R C N C R R O C R H 2 C=CH 2 H 2 C=NH H 2 C=O Bond angle 120 o sp 2 Hybridization : Trigonal Planar
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10 Chem 266 Reviews
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11 Chem 266 Reviews FB F F empty 2p orbital
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12 Chem 266 Reviews
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13 Chem 266 Reviews Breaking π bond: very difficult
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14 R N R R O R R C R R R R Tetrahedral Bent Bond angle between R groups approx 109 0 bond angle 109.5 0 CH 4 NH 3 H 2 O Trigonal pyramidal bond angle 107 0 bond angle 104.5 0 Chem 266 Reviews sp 3 Hybridization : Tetrahedral
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15 Chem 266 Reviews Experimental Result VB 1s 2 2s 2 2p 2 energy Catom 1s 2 2s 1 2p 3 But 2s and 2p orbitals are different!
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This note was uploaded on 07/07/2010 for the course CHEM 267 taught by Professor Fang during the Winter '09 term at Waterloo.

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1_Delocalized_System - CHEM 267 Basic Organic Chemistry 2...

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