Ch. 14 & 15 Topics and Tips

Leader: Hannah J.
Course: Chem 331
Supplemental Instruction
Instructor: Dr. Winter
Iowa State University
Date: 12/4/15
The following is a (checkable) list of the topics from Ch. 14 and 15 you should know and
understand for Exam 4 and the Final Exam.
Ch. 14 & 15 Topics and Tips
Ch. 14: Conjugated Alkenes
 Definition of conjugation and identifying conjugated and non-conjugated alkenes
 Know that conjugated are more stable than non-conjugated and why (as it relates to
resonance and heat released by each)
 Reaction & Mechanism: Reactions of Dienes with HX
o 1,2-addition and 1,4-addition and their products (mixture)
o Kinetic and Thermodynamic Products and which is present at high and low
o How this all relates to an energy diagram of 1,2- and 1,4-addition
 Diels-Alder Reaction & Mechanism
o Identifying diene and dienophile, the meaning of each name, and which should be
electron-rich and electron-poor (nucleophile or electrophile) for the best DielsAlder reaction
o Know examples of electron-donating and electron-withdrawing groups and that
EDG (electron-donating groups) go on dienes and EWG (electron-withdrawing
groups) go on dienophiles and why (in terms of electron-rich/poor)
o The two traits that contribute to a group’s overall electron-donating or electronwithdrawing characteristic (electronegativity (i.e. the inductive effect) and
resonance) and how they contribute or take away electron density in EDG and
o Know that dienes react for Diels-Alder reactions only in the s-cis conformation
(Cycle dienes are the best because they are “locked” in this conformation; in
straight-chain dienes, only a small fraction will be in the reactive s-cis
conformation at any given moment because it is less stable than s-trans)
o The Diels-Alder reaction always forms a 6-membered ring with a double bond (a
cyclohexene). This double bond will always be between C’s 2 & 3 if you use the
numbering system from Dr. Winter’s lectures. Anything else you see in the
product is simply a substituent off of this ring and should also appear somewhere
in your reactants.
o Bicyclic rings are simply a fusing of two rings; they are only formed when the
diene is cyclic (in a ring). These are represented as a 1- or 2-C bridge above the
normal cyclohexene connected at C1 and C4 (in Dr. Winter’s numbering system).
Think of them as another substituent to the basic ring.
o Stereochemistry of Diels-Alder reactions and the Endo Rule: Know the conditions
for which the Endo Rule applies and how the stereochemistry should look when
the Endo Rule does or does not apply
o Don’t be thrown by the 3-D representations of the product; these are
interchangeable with their flat counterparts. You could be given either on an exam
1060 Hixson-Lied Student Success Center  515-294-6624  
and asked to fill in the reactants, but if you are asked to fill in the product(s), you
can choose if you would rather give it/them in the flat or 3-D version.
o There are a number of ways that Diels-Alder reactions can vary. Practice
problems with triple bonds, multiple equivalents of a reactant, filling in either the
reactants or the products, etc., and make sure that you know the mechanism and
your numbering system well so that you can predict the missing pieces in a new
Ch. 15: Aromatics
 Memorize the common names and the corresponding structures of the seven common
aromatics given in class 12/2/15.
 Nomenclature:
o Know the 3 positioning names (ortho, meta, and para) and which corresponds to
which position. In most cases, numbering is not needed for aromatics because
these positioning names are used instead.
o Practice giving missing IUPAC names or structures for aromatic compounds. Get
comfortable combining the positioning and 7 memorized common names with the
substituent names we’ve learned in past units into a single name or structure.
 Not all rings with alternating double bonds are aromatic! Know the requirements for
aromaticity and anti-aromaticity and the special stability or instability of each type.
 Practice identifying molecules as aromatic, anti-aromatic, or neither.
o Exception to normal sp3 hybridization rules: a lone pair next to a double bond will
re-hybridize to sp2 (for increased stability of conjugation)
o Know what to do when heteroatoms (O, N, S) with lone pairs show up in the
structure: If the heteroatom is part of a double bond, the pi orbitals are already
used, so the lone pairs are not in the pi system. If the heteroatom is not part of a
double bond, it can contribute a maximum of one lone pair to the pi system (to
your count of pi electrons in requirement 4).
o Be familiar with how charges affect a structure’s aromaticity in terms of
hybridization and/or pi electrons (for requirements 3 & 4)