Chemistry 227 Chapter Notes

Chemistry 227 Chapter Notes (Solomons 9e)

Chapter 1 Notes

Homework: 1.16, 17, 18, 19, 20, 21, 22, 24, 26, and 32

Some background

• What is vitalism ?

• What did Stanely Miller do in the 1950’s?

• What are organic compounds ?

• How did we get from such a barren planet to a planet with an unending variety of organic compounds ?

• What did Lavoisier, Wohler, Avogadro and Kekule contribute to organic chemistry ?

• What are isomers in general ?

• What are constitutional isomers ?

Bonding and the shape of molecules

• bonding: ionic and covalent.

• Lewis structures and VSEPR models also explain and predict geometry about the central atom for covalent compounds. Be especially familiar with AX₂E₂ , AX₃E, AX₄.

• Resonance, resonance hybrid and how to move electrons around to convert one resonance contributor to another.

• Be able to calculate formal charge on atoms in a moleule.

• Polarity of bonds is determined by the electronegativity difference of the two atoms.

• Polarity of molecules is determined by three dimensional arrangement of the bonds in the molecule.

How can these shapes be explained by quantum mechanics ?

• The tetrahedral molecular geometry around certain central atoms like C, N, O can be explained by quantum theory which mathematically mixes s, p_x, p_y, and p_z atomic orbitals to make the hybridized tetrahedral sp³ molecular orbital.

• Be able to identify molecules as an alkane, alkene or alkyne.

• Be able to draw the atomic orbitals AO’s for carbon (1s, 2s and 2p set).

• Be able to draw the hybridized molecular orbitals MO’s for sp³, sp² and sp carbon.

• Be able to use the MO’s to explain observed geometries for sp³, sp² and sp carbon.

• Know rough bond angles for sp³, sp² and sp carbon (i. e. 109°, 120°, 180°).

• saturated versus unsaturated

• sigma (s) bond and pi (p) bond

Chapter 2 Notes

Homework: 2.27, 28, 29 (c, d, and i only), 31, 33, 34, 42 (wow!).

• What is a functional group ?

• Know these functional groups: alcohol, carboxylic acid, alkene (double bond), alkyne (triple bond), phenyl group and halogen.

• Be able to identify 1°, 2°and 3° carbons in molecules.

• What is an alkyl halide ?

NOTE: IR spectroscopy (Section 2.16) will be covered in greater detail in CHEM 228

Chapter 3 Notes

Homework: 3.21, 22, 25, 26, 29 and 31

• Be able to identify a reaction as a substitution, elimination, addition, or rearrangement.

• Homolytic and heterolytic bond cleavage.

Where do the electrons go ?

What is a radical, carbanion and carbocation ?

When to use double headed arrows () and single headed arrows ().

You will be provided a list of acids and pK_a’s.

• Predict the outcome of a acid base reaction. “Will this reaction take place ?”

• Understand resonance and inductive effect and be able to use it to predict acid strength.

• Isotopic labeling. What is it ? How can you replace a Br in an alkyl bromide with a D or T ?

• Use curvy arrow notation to explain the mechanism of a reaction.

Chapter 4 Notes

Homework: 4.22, 23, 24, 33, 39, and 44.

• Know the IUPAC names of all of the unbranched (normal) alkanes from CH₄ , methane, to CH₃CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH_3
,dodecane.

• Be able to deduce the IUPAC names for branched alkanes, haloalkanes, alcohols, diols, monocyclic compounds.

• Know the IUPAC names of groups derived from the straight chains from CH₃ -, methyl, to CH₃CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂-, dodecyl.

• Be able to deduce the IUPAC names of groups derived from the branched chains. For example

• Be able to identify primary (1°), secondary (2°), tertiary (3°) and quaternary (4°) carbons

• Trends in physical properties: boiling point, melting point.

• Conformational analysis:

- Newman projections

- conformations: staggered, eclipsed, anti, gauche.

- torsional strain

• Monocyclic alkanes.

- angle strain

- torsional strain

- cyclohexanes

- conformations: boat, chair.

- axial and equatorial positions

- cis and trans isomers

• Know (memorize) the common names of the molecules and groups below. The n - is optional.

Chapter 5 Notes

Homework: 5.30(a-d), 31, 33, 35 and this page.

• Be able to determine if a object (especially a molecule) is chiral or achiral.

• Know the difference between stereoisomers and constitutional isomers.

• Be able to determine if two compounds (including cyclic compounds) are enantiomers, diastereomers or the same compound.

• Be able to identify meso compounds and know that meso compounds have 2 or more stereocenters but are not chiral.

• What is the relationship among physical properties (e. g. boiling point), optical rotation, enantiomers and diastereomers ?

• Be able to assign R or S to stereocenters.

• What is the maximum number of stereoisomers are possible a molecule that has with n stereocenters ? answer = 2ⁿ

• How is optical rotation (observed and specific) determined ?

• Know the following solutions: racemic, scalemic, optically pure.

• Know the relationship among enantiomeric excess (ee), the percentages of each enantiomer (e.g. A and B) present, and specific rotation [a] using the formulas: and

[a]_mixture = ee[a]_pure

• Be able to use R and S (as well as + and - when known) in naming optically active compounds.

Chapter 6 Notes

Homework: 6.13, 14, 15 (b, c, d), 17, 18, 21 (e, i), 22, 31, and 32.

• Know mechanisms for the SN1, SN2, E1, E2 reactions.

• What stabilizes a carbocation ?

• Free energy diagrams for exergonic and endergonic SN2 reactions. What does the transition state of the SN2 reaction look like ? What is DG° and DG^‡

• Know the stereochemistry of the SN1 and SN2 reaction.

• How can structure of the substrate, strength of nucleophile, solvent and nature of the leaving group affect the rate of the substitution reactions ?

• Which reaction mechanism will be favored. Predict the major and minor products of a reaction. See below

alkyl halide substrate	favored reaction
methyl halide, CH₃X	SN2 only
1°, CH₂RX	SN2 dominates. E2 can be encouraged by using a strong bulky (or hindered) base like (CH₃)₃CO^-
2°, CHR₂X	SN2 dominates especially with weakly basic nucleophiles like I-, CN- and RCOO^-. E2 can dominate if strong bases like RO^- and especially if a bulky base is used.
3°, CR₃X	No SN2. E2 will dominate if a strong base (especially a bulky base) is used. At other times there is competition between SN1 and E1 which can be influenced by temperature and other factors.

reaction	when favored
SN1	3° substrate, weak nucleophile/base (e.g. ROH, HOH, NH₃, F^-), polar protic solvent, low temperatures. The SN1 rate is proportional to the polarity of the solvent .
SN2	methyl halide, 1° or 2° substrate, weakly basic nucleophiles (e.g. I^-, CN^-, RCO₂^-) polar solvent. SN2 rate is faster in polar aprotic solvent
E1	3° substrate, weak nucleophile/base (e.g. ROH, HOH, NH₃, F^-), polar protic solvent, high temperatures.
E2	3° substrate, strong base (especially a bulky base) polar protic solvent.

Chapter 7 Notes

Homework: 7.18 - 24, and 26.

• Nomenclature of alkenes and alkynes.

• Know the vinyl and allyl group.

• Know how to use cis and trans as well as E and Z.

• How do catalysts work in terms of activation energy (DG^‡) ?

• Catalytic hydrogenation of alkenes.

- What is the mechanism of the transition metal hydrogenation catalysis ?

- What is the stereochemistry of alkene hydrogenation reaction ? (syn addition)

• Catalytic hydrogenation of alkynes.

- How does catalyst choice determine the stereochemistry of alkyne hydrogenation reaction ?

H₂/Ni₂B

H₂/Pd/CaCO₃ (Lindlar’s Catalyst)

syn addition = Z (or cis) alkenes

(1) Li, C₂H₅NH₂

(2) NH₄Cl

anti addition = E (or trans) alkenes

• Stability of substituted alkenes

• Stability of cycloalkenes and cycloalkynes

• Synthesis of alkenes by dehydrohalogenation reactions

- E2 mechanism dominates (anti periplanar transition state).

- A mixture of products is common.

- Zaitsev rule when small bases like EtO^- are used.

- Hofmann rule when bulky bases like (CH₃)₃CO^- are used.

• Synthesis of alkenes by dehydration of alcohols

- Acid catalyzed.

- E1 mechanism dominates.

- A mixture of products is common.

- Zaitsev rule is followed most often.

- Alkyl and hydride migration will occur when possible to make a more stable carbocation intermediate.

• Synthesis of alkenes by debromination of vicinal dibromides

- By Zn or NaI

- Know mechanism and stereochemistry (anti periplanar) when using NaI.

• Using sodium in liquid ammonia (i.e. NaNH₂ is the base) to generate sodium acetylides.

• Using sodium acetylides as nucleophiles with primary alkyl halides.

Chapter 8 Notes

Homework: 8.27(a-l), 28(a-l), 29, 30, and 32.

• Know the regiochemistry (e.g. Markovnikov or anti-Markovnikov) and stereochemistry (e.g. syn addition or anti addition or racemic mix) of the following additions to alkenes and alkynes. Pages 358 and 359 "summaries" might be helpful. Be able to write the mechanism for each *ed reaction.