Review of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus Ethylene
Trang 1I Review of Lewis Bonding Theory
A Ionic Bonding
B Covalent Bonding
1 Multiple Bonding
2 Formal Charge
C Short-Hand for Chemists
1 Line-Angle Formulas
2 Dashes and Wedges
3 Curved Arrow Formalism
II Resonance
A Drawing Resonance Structures
B Energy of Resonance Structures
C Structure and Reactivity from Resonance
III Review of Molecular Orbital Theory
A Atomic Orbitals
B Sigma-Bonding
C Pi-Bonding
D VSEPR Theory
IV Hybridization/LCAO
A sp Hybridization
B sp2 Hybridization
C sp3 Hybridization
I Review of Lewis Bonding Theory
A Ionic Bonding
B Covalent Bonding
1 Multiple Bonding
2 Formal Charge
C Short-Hand for Chemists
1 Line-Angle Formulas
2 Dashes and Wedges
3 Curved Arrow Formalism
1 Provide all of the valid Lewis structures for the
following molecules
2 Convert the following to line angle formulas
You need to be able to:
• Provide Lewis structures and line angle formulas
for given molecular formulas Don't forget lone pairs and formal charges!
• Draw/interpret 3-D structures with dashes and wedges
• Draw curved arrows to represent simple reaction
mechanisms Hint: You will frequently start an arrow on a negative charge (electrons!) , but never start an arrow on a positive charge (no electrons!)
3 a) Provide a mechanism for the following
reaction
H 3 C O H 2 C Cl H 3 C O CH 3 Cl
b) Label the electrophile and the nucleophile
Trang 2II Resonance
A Drawing Resonance Structures
B Energy of Resonance Structures
C Structure and Reactivity from Resonance
You need to be able to:
• Recognize resonance structures
• Interconvert resonance structures
• Predict relative energies and importance
• Predict reactivity/physical properties using resonance structures
H3C N CH2
O
CH3
H 3 C N CH3
O
CH 3
H 3 C CH 3
O H
H 3 C CH 3
O H
1 For each pair, circle the most stable
resonance structure, and use curved arrows to
convert the structure on the left to the structure
on the right
2 Provide all relevant resonance structures for the
following molecules, and rank their energies
N
N H H
O
H 3 C
O CH3
Hint: Generating charges is bad!!
• When you start with a neutral molecule, don't generate more than two formal charges
• When you start with a charged molecule, don't generate any other formal charges
Delocalization = Stabilization
III Review of Molecular Orbital Theory
A Atomic Orbitals
B Sigma-Bonding
C Pi-Bonding
D VSEPR Theory
IV Hybridization/LCAO
A sp Hybridization
B sp2 Hybridization
C sp3 Hybridization
1 Rotation of Ethane versus Ethylene
You need to be able to:
• Draw atomic orbitals (s, p)
• Draw hybrid orbitals (sp, sp2 , sp3)
• Differentiate between σ- and π-bonding
• Assign hybridization to atoms in a molecule
• Predict approximate bond angles
• Draw simple molecular orbital pictures
1 Draw the bonding and anti-bonding orbitals
resulting from the combination of two py
orbitals along the x-axis Label any nodes Is
this σ- or π-overlap?
2 Try to do the same with a px and a py orbital
Why doesn't this work?
3 a) Draw a molecular orbital picture of the
following molecule
b) Use the picture from part a to explain why the
following equilibrium does not occur
CH
Trang 3V Properties of Molecules
A Acidity of Organic Molecules
1 Bronsted–Lowry Acidity
a) Review of Acid/Base Equations
b) Acidity Trends
i) Attached Atom
ii) Inductive Effects
iii) Hybridization
iv) Resonance
2 Lewis Acidity
B Bond Lengths
C Bond Strengths
You need to be able to:
• Correlate Ka, pKa, and acidity
• Rank relative acidities and explain your reasoning
• Differentiate between Bronsted-Lowry and Lewis acids and bases
• Draw mechanisms for acid-base reactions
• Rank bond lengths and strengths based on bond order
1 Which of the following molecules can act as
a Lewis base? Why?
Me 3 N BF 3 H 2 O CH 4
2 The following pair can undergo a
Bronsted-Lowry or a Lewis acid-base reaction Provide the
products for both, and use curved arrows to
provide the reaction mechanisms
O
CH3
3 Rank each series by acidity (1 = most acidic)
H2N H HS H
HO H a)
b)
F3C O
O
H
H3C O
O
H
H3C
O
O
H
c)
H3C CH2
H
H2C CH
H
HC C H
A Molecular Formulas
1 Degrees of Unsaturation • Draw constitutional isomers for a given molecular formula
2 Constitutional Isomers • Calculate degrees of unsaturation
B IUPAC Nomenclature • Draw structures corresponding to IUPAC names
C Conformational Analysis • Draw Newman projections
1 Ethane • Determine relative energies of rotational conformers Know
a) Newman Projections the rotational energy values on the handout!
2 Propane • Draw potential energy diagrams for bond rotations
3 Butane
1 Draw all of the constitutional isomers of C5H12 3 a) Approximate the barrier to rotation around
and name them using IUPAC nomenclature the C2–C3 bond of 2,2-dimethylbutane Draw
Newman projections to illustrate your answer
2 For each molecular formula, calculate the
degrees of unsaturation and draw two possible b) Draw a potential energy diagram for rotation constitutional isomers around theC2–C3 bond of 2,2-dimethylbutane
Trang 95.12 Spring 2003 Review Session: Exam #2
1 Degrees of Unsaturation 1 Cahn–Ingold–Prelog Convention (R/S)
2 Constitutional Isomers 2 Optical Activity
C Conformational Analysis D Diastereomers
a) Newman Projections 2 Molecules with >1 Stereocenter
A Ring Size and Strain B Review of Thermodynamics
1 Conformational Analysis 3 Hammond Postulate
2 Mono-Substituted Cyclohexane E Chlorination of Propane
a) Axial versus Equatorial: A-Values 1 Inequivalent Hydrogens (1°,2°,3°)
3 Di-Substituted Cyclohexane 2 Relative Reactivity
b) Preferred Conformers F Bromination of Propane
4 Bicyclic Ring Systems 1 Selectivity (Hammond Postulate)
VIII Stereochemistry G Radical Stability
A Stereoisomers H General Selectivity of Radical Halogenations
VI Alkanes You need to be able to:
A Molecular Formulas
1 Degrees of Unsaturation • Draw constitutional isomers for a given molecular formula
2 Constitutional Isomers • Calculate degrees of unsaturation
B IUPAC Nomenclature • Draw structures corresponding to IUPAC names
C Conformational Analysis • Draw Newman projections
1 Ethane • Determine relative energies of rotational conformers Know a) Newman Projections the rotational energy values on the handout!
2 Propane • Draw potential energy diagrams for bond rotations
3 Butane
1 Draw all of the constitutional isomers of C5H12 3 a) Approximate the barrier to rotation around and name them using IUPAC nomenclature the C2–C3 bond of 2,2-dimethylbutane Draw
Newman projections to illustrate your answer
2
degrees of unsaturation and draw two possible b)
constitutional isomers around theC2–C3 bond of 2,2-dimethylbutane
C 7 H 12 C 3 H 6 C 5 H 6
*The solutions for these problems can be found
in the key for the first review session
Trang 10You need to be able to:
• Provide the approximate ring strains and preferred conformations of the rings discussed in class
• Analyze ring strain in terms of torsional and angle strain
• Draw Newman projections to compare conformations of cycloalkanes
• Draw and flip cyclohexane chairs Be sure you carefully
differentiate between axial and equatorial bonds
• Provide the details of a cyclohexane ring flip
• Use A-values and diaxial interactions to predict the
preferred conformers of substituted cyclohexanes Know
your A-values!
• Draw and differentiate between cis- and trans-isomers
2 Draw chair conformers for cis- and trans-decalin
Which would you expect to be more stable?
VII Cycloalkanes
A Ring Size and Strain
B Cyclopropane
C Cyclobutane
D Cyclopentane
E Cyclohexane
1 Conformational Analysis
a) rawing Chairs
b) Ring Flip
2 Mono-Substituted Cyclohexane
a) xial versus Equatorial: -Values
3 Di-Substituted Cyclohexane
a) is/Trans Isomerism
b) Preferred Conformers
4 Bicyclic Ring Systems
H
H
H
H
3. Using Newman projections, predict the energy
difference between the two Hint: Look for
gauche-butane interactions in the higher energy structure
1 Draw the two possible chairs for each molecule,
and indicate the preferred conformer
Me
Me
Me
Et Which molecule would you expect to have
the largest conformational preference Why?
D
C
You need to be able to:
• Recognize stereoisomers: enantiomers & diastereomers
• Draw all possible stereoisomers for a given molecule:
Remember the 2 n rule
• Determine whether molecules are chiral or achiral: a)
Count stereocenters; b) Look for mirror planes; c) Compare mirror images
• Recognize meso compounds
• Assign R/S stereochemistry to stereocenters
• Correlate chirality with optical activity
• Describe ratios of enantiomers using optical activity ( optically pure, racemic, etc.)
1 Draw all of the stereoisomers of 1,2- and
1,3-dimethylcyclohexane Assign each stereocenter
as R or S How many are chiral? Achiral?
Try to draw a chiral stereoisomer of
1,4-dimethylcyclohexane Can you do it? Why or
why not?
VIII Stereochemistry
A Stereoisomers
B Chirality and Stereocenters
C Enantiomers
1 Cahn–Ingold–Prelog Convention (R/S)
2 Optical Activity
3 Description of Samples
D Diastereomers
1 Cis/Trans Isomers (Geometric)
2 Molecules with >1 Stereocenter
3 All of the above molecules are achiral; however, hexahelicene (below) is chiral Why?
Hexahelicene
2 Practice assigning R and S stereochemistry
until you feel like your head will explode!
There are ample examples in the book and
lecture
Trang 11IX Free Radical Reactions
A Chlorination of Methane
1 Mechanism
B Review of Thermodynamics
1 Thermodynamic Control
2 Kinetic Control
3 Hammond Postulate
4 Multi-Step Reactions
5 Chlorination of Methane
E Chlorination of Propane
1 Inequivalent Hydrogens (1°,2°,3°)
2 Relative Reactivity
3 Selectivity
F Bromination of Propane
1 Selectivity (Hammond Postulate)
G Radical Stability
H General Selectivity of Radical Halogenations
You need to be able to:
• Write a complete mechanism for a free radical chain
reaction Use fishhook arrows!
• Draw and completely label a reaction-energy diagram
• Determine the rate-determining step of a multi-step reaction-energy diagram
• Differentiate between transition states and intermediates
• Differentiate between kinetic and thermodynamic control
• Use the Hammond postulate to predict whether a kinetically controlled transformation will be selective
• Use BDEs to estimate ∆H and ∆G
• Rate the stability of radicals, and explain
• Predict the products of radical bromination
• Calculate the relative reactivity of inequivalent hydrogens from reaction selectivities
1 Radical stability is strongly dependent on
substitution (3° > 2° > 1° > methyl) hy?
Draw pictures to illustrate
2 Draw resonance structures to explain the
selectivity of the following reaction
CH3 Br2
hv
Br
4 Rank the stability of each of the following radicals (1 = most stable) Radicals with the same energy should be given the same number
H3C
H3C
CH3
Aside from resonance, why isn't the following
product observed?
CH3
3. Provide a complete reaction mechanism for
the bromination in number 2 Draw a complete
reaction energy diagram for the propagation steps ou can assume that a benzylic C–Br bond is approximately 68 kcal/mol
W
Y