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Chapter 2 Summary-Summer 2014
Homework: 27 i and ii for all parts, 28 (you must write out the Lewis structures of each species before beginning this
problem or you will be lost), 29 all but d, 30 all but d, 31 all but f, 32, 33 (remember opposite charges attract! Note that you
might have to peak at the solutions to get the structures of some of the species), 34-37, 38 (as many as you can without
going nuts), 39, 40 (just give the IUPAC names), 41, 42, 45, 46 (just give the IUPAC names), 52-56.
2.1: Kinetics and Thermodynamics of Simple Chemical Processes. Read this section for QUALITATIVE terminology
purposes. You do not have to do any of the calculations. Read to understand the following bulleted items and lecture
material.
 You should know the difference between thermodynamics and kinetics.
o Thermodynamics refers to the changes in energy as reactants are converted into products. These energy
changes impact the position of equilibrium (will the reactant or products be favored at equilibrium? etc.)
o Kinetics refers to how fast a reaction reaches equilibrium (which depends upon the activation energy of
the rate determining step and the concentration of reactants involved in the rate determining step).
 You should qualitatively know this equation: G = H – TS.
o Based upon general chemistry material you should know that G is called the Gibbs Free Energy Change
for a reaction. For a reaction to be spontaneous (where the products are favored at equilibrium) the G
value for that reaction must be negative.
o You should also know that the enthalpy change (H) has to do with the bond energies of bonds broken
minus the bond energies of the bonds formed in a reaction (see the very top of page 52).
 Exothermic reactions (negative, heat energy released) are where the bond energies of bonds
formed are stronger than the energies of bonds broken. Endothermic reactions are the opposite.
o You should know that the entropy change (S) has to do with the relative “order” of the reactants vs. the
products. If a reaction goes to more disorder it is more likely (not definitely) to be spontaneous (and thus
have a negative G).
 You should be VERY comfortable with the diagram (and all associated terminology) in Figure 2.1 on page 53.
o You should know the following terms: Potential Energy Diagram, Reaction Coordinate, Transition state
(TS), Enthalpy Change (H), Activation Energy (Ea).
o Don’t worry about defining the Boltzmann distribution or knowing the Arrhenius Equation on an exam.
However, you should conceptually know that the consequences of these two concepts are:
 The speed of a reaction is impacted by the activation energy of the rate determining step (we
will discuss this in much greater detail in chapter 6). You should know that the more energy the
molecules have (due to higher reaction temperatures) the more likely an activated complex can
“get over” the activation barrier. This is why reactions tend to speed up at higher temperatures
(see Figure 2.2 and the Boltzmann distribution)
 You should know that a reaction will be faster if the species involved in the rate determining
step of that reaction are present in higher concentrations.
2.2: Acids and Bases: THIS SECTION IS VERY VERY IMPORTANT. Learn it NOW - or you will be HAUNTED
for the rest of your organic chemistry lifetime! Do exercises 7 (hint: draw all lone pairs in your Lewis structures), 8, 9,
10, 11, 13, 14, 15
 Read over the first subsection to refresh your memory about acid-base equilibria.
o Notice the arrow pushing mechanisms illustrated for two proton transfer reactions in the middle of page
57.
 Read over the second subsection to get oriented to pKa terminology.
o Remember the larger a Ka value, the more products are favored at equilibrium.
o While no calculations are required knowing that pKa = -log Ka will help you remember that large Ka
values will convert to very small pKa values. You should burn into your brain that the lower the pKa
value the stronger the acid.
 Memorize the pKa values of the asterisked acids in the salmon pKa class hand-out (also at the last two pages of
this summary sheet).
 Read the third and fourth subsections as if they were the most interesting and exciting chemistry text you have
ever read. KNOW these subsections. They are very important.
o I promise that in the very near future you will be required to explain “apples to apples” relative acid/base
strengths. Acceptable explanations will compare conjugate base structures and discuss things such as
molecular structure, atomic size, electronegativity, hybridization, and resonance. An acceptable
explanation will NOT simply say that a certain acid has a lower pKa and thus is a stronger acid.
 Read over the terminology in the fifth sub-section:(Electrophiles and Nucleophiles….). These terms will become
very important in chapter 6 and then remain important for the rest of your organic chemistry career.
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2.3: Functional Groups (This is a busy-work memorization section)
 It is important to be able to “pick-out” the functional groups in any given molecule because this will allow you to
be able to predict which type of chemistry this molecule will undergo (once you know each functional group’s
chemistry!)
 Right now, memorize all the functional groups listed in Table 2.3. After a while this memorization should become
instinctual.
 I will probably have a problem on the exam where you are required to circle and identify the functional group or
groups present in a molecule.
 Know that “R” is simply a generic representation of some alkyl group.
 Note that an alkyl group or an alkane is generally not considered as a functional group due to lack of chemistry. Of
course, we will spend chapter 3 looking at the “chemistry” of alkanes…but even so, alkanes are generally ignored
when you are identifying functional groups in a molecule (like on an exam)
2.4: Straight Chained and Branched Alkanes. Do exercise 16a (it is best to do this problem AFTER you learn
nomenclature. This will allow you to recognize some of your proposals as identical molecules drawn a little
differently). Be sure to practice bond-line representations.
 Know the general formula for straight-chain and branched alkanes is CNH(2N+2). Where N = # carbons.
 Know what is meant by the term "constitutional isomers"
 Go back to the end of chapter problems in chapter 1 and do problem #45.
 You should also be able to do end of chapter problems for chapter 6 on page 246: #31, 32, and 33.
2.5: Naming alkanes Do exercises 17, 18 (but also do for carbons), 19, 20
KNOW THIS SECTION: This is not a hard section but you need to be very "anal retentive" when you study it.
 Memorize the series C1 to C20 (methane to icosane in Table 2.5).
 Learn the tert- and iso- prefixes. They are too common to ignore.
 Learn to distinguish between primary, secondary, tertiary, and quaternary carbons.
 Learn the IUPAC rules for naming branched alkanes.
 Be able to go from Bond-line formulas to an IUPAC names.
 Be able to go from IUPAC name to a Kekule/condensed or bond-line formulas.
 Know primary (1o), secondary (2o), tertiary (3o), and quarternary (4o) terminology.
 Ignore the very last column in Table 2.6. I don’t think identifying branches as primary, secondary is useful.
2.6: Structural and Physical Properties of Alkanes. Lightly read over this section. (Do exercise 21)
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Understand that the bp of a substance is related to the amount of energy needed to break all intermolecular forces
between molecules in the liquid phase. If a particular substance has strong intermolecular forces than it will have a
high bp.
You should understand the boiling points discussion from chapter 6 section 1 based upon this material.
Understand that the more surface area a molecule has the more chances there are for intermolecular London
interactions. Thus, straight chain alkanes (having lots of surface area) have higher boiling points than spherical
alkanes (having less surface area) of similar molecular weight.
Conversely, the more spherical a molecule is the better it packs into a solid lattice. Thus, more spherical molecules
(of similar molecular weight) have higher melting points.
2.7: Rotations about Single Bonds: Conformations. Read this very short section very carefully.
 Everything is this section is important. All terminology is important. This material will be fundamental to section
8.
 Pay careful attention to the Figures in this section.
 You need to become very comfortable with Newman Projections. PRACTICE PRACTICE PRACTICE!
2.8: Rotation in Substituted Ethane’s. Read this section very carefully. Your success in this section
depends upon your understanding of section 7. (Do exercises 22, 23).
 All terminology and All Figures are very important.
 Spend a lot of time on this section.
 Do a diagram for pentane. One along the C2-C3 bond axis. Another along the C3-C4 bond axis. Label all
projections as eclipsed, staggered, or gauche.
 Distinguish between electronic repulsion from steric versus torsional strain
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pKa Values of selected acids
-
HA
A
(* Memorize the pKa values to the nearest whole number for asterisked acids. Understand trends for all acids. Note: The
first question on every exam might ask you the pKa for an asterisked acid.) ** Memorize for organic II only…not organic I.
Halogen Acids
Acid
Conjugate Acid
*HI
*HBr
*HCl
HF
pKa
-10
-9
-8
+3.2
Conjugate base
Base
IBrClF-
Other Strong Inorganic Acids
Acid
Conjugate acid
H2SO4
*H3O+
HNO3
pKa
-3
-2
-1.4
Conjugate base
Base
HSO4H2O
NO3-
Weak Inorganic Acids
Acid
Conjugate acid
H2S
*NH4+
*NH3
*H2O
pKa
+7
+9
+35
+16
Conjugate base
Base
HSNH3
NH2HO-
Organic Oxyacids Acids: Alcohols
Acid
pKa
Conjugate base
Conjugate acid
Base
*ROH2+
-2
ROH
+16
RO*ROH
Note: “R” is a generic representation for various alkyl groups. The bulk of the alkyl group can
impact acidity but for a ballpark pKa value +16 works.
NOTE:
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The smaller the value of the pKa the more acidic the acid (the stronger acid)
The more Acidic an acid is the more stable its conjugate base.
The less Acidic an acid is the less stable its conjugate base.
A more stable base (a weaker base) has a more acidic conjugate acid relative to a less stable base.
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Organic Acids: Other Oxyacids
Acid
ConjugateAcid
O
R
Base
* generic
*
OH
OH
ConjugateBase
pKa
O
+5
R
R = CH3 pKa = +4.7
O
O
+10
*
O
SOH
*
CH3
O
O
SO
-3
O
CH3