CH 1 2 3 4 Important Points.docx - Important Points Chapter 1 Structure and Bonding Organic Chemistry is complex and mastering organic chemistry is

CH 1 2 3 4 Important Points.docx - Important Points Chapter...

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Important Points: Chapter 1: Structure and Bonding Organic Chemistry is complex and mastering organic chemistry is based on understanding the principles and applying them extensively. To succeed it helps to simplify the complexity by a) Understanding Trends b) Keep careful track of electron density ( electrons) in all cases Hybridization, Geometry and Bond angle Relationships HYBRIDIZATION Of the CENTRAL ATOM NUMBER OF HYBRID ORBITALS Bonds+L P ELECTRON GEOMETRY MOLECULAR GEOMETRY EXAMPLE BOND ANGLE in degrees sp3 4 4 Tetrahedral Tetrahedral trigonal pyramidal bent CH4 (0 LP) NH3( 1 LP) H2O ( 2LP) 109.5 sp2 3 3 Trigonal planar Trigonal Planar or bent BCl3 (0 LP) Each C atom in C2H6 120 sp 2 2 Linear Linear Each C atom in C2H2 (0 LP) 180 LP = Lone Pairs The hybridization of an atom is important to know because it affects- The geometry ( bond angle ) of that part of the molecule – later on you will see how bond angle may control whether a reaction proceeds or not, and may affect the stereochemistry of the products) SIGMA VS PI BOND
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BOND TYPE OVERLAP Sigma END-ON Always the first bond between 2 atoms is a sigma bond. There can only be 1 sigma bond between 2 atoms Rotation about the bond is allowed Sigma bonds cannot be changed between different resonance structures because that would mean the sigma bond will be broken Pi SIDEWAYS Additional bonds between 2 atoms will be pi bonds. Double therefore consist of 1 sigma and 1 pi bond Triple Bonds consist of 1 sigma and 2 pi bonds Rotation about a pi bond is NOT allowed because it would break the pi bond Resonance Structures can involve the re- arrangement of pi bond electrons or lone pair electrons. BOND MULTIPLICITY BOND ORDER No of SIGMA BONDS No of PI BONDS BOND STRENGTH BOND LENGTH 1 ( Single Bond) 1 1 0 LEAST LARGEST 2 ( Double Bond) 2 1 1 3 ( Triple Bond) 3 1 2 LARGEST LEAST BOND STRENGTH IS GREATER THE GREATER THE S CHARACTER OF THE HYBRIDIZATION OF THE ATOMS OF THE BOND SP3 HAS THE LEAST S CHARACTER, SP2 IS MEDIUM AND SP HAS THE MOST S CHARACTER THE C-C BOND IN CH3-CH3 IS AN SP3-SP3 BOND SO IS RELATIVELY WEAK.
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DRAWING AND INTERPRETING CHEMICAL STRUCTURES ( SEE SEC 1- 12 IN THE TEXTBOOK ) A) Kekule Structure B) Condensed Structure C) Skeletal or Line-Bond Structure You should be able to go between the different structures. To interpret structures correctly you need to be able to quickly figure out how many H atoms are on each C ( C with no formal charge can have 4 bonds max, so the no of H atoms on every carbon atom is such as to make the total number of bonds on each C atom equal to 4) CH 2: POLAR COVALENT BONDS; ACIDS AND BASES ELECTRONEGATIVITY, BOND POLARITY, MOLECULAR POLARITY AND THEIR CONSEQUENCES ELECTRONEGATIVITY (EN) TRENDS: A)
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