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Chemistry 242
Final Exam
Summer 2010
The final exam for this course will be on Friday, Aug. 6. It will be on the material in Chapters 10 – 21,
24, and 25 that we have covered in class
The following text section will be covered on the exam. (Bold indicates change from hourly exams.)
Chapter 10: all except 10.9
Chapter 11: all except 1, 12 and 13
Chapter 13: sections 13.8 – 13.11 only
Chapter 14: section 14.1 only
Chapter 15: sections 2, 3, 5, 6, and 10 only
Chapter 16: all except 16.8, 16.9
Chapter 17: all except 17.10, 17.11
Chapter 18: sections 1, 2, 3
Chapter 19: all except 9, 10, 12 – 15
Chapter 20: all except 20.5
Chapter 21: all except 21.8, 21.9
Chapter 24: sections 1 – 4 and 6 only
Chapter 25: sections 1, 3, 5, 9, 10 only
It is especially important to study and do the problems for the following sections:
10.4 10.5
10.7
11.4
11.5 11.11
18.3
13.8 13.9
13.11
14.1
15.3
15.5
16.1 16.5
16.6
17.4 to 17.7 17.6
19.4 19.8 19.11
20.6
21.2 21.3 21.6
24.6
25.10
Topics that may be covered on the final
Names for functional groups covered this semester.
Free radical halogenation of an alkane (ex: Cl2/uv light). Which radical is most stable?
Allylic bromination of an alkene. Draw out resonance forms for the allylic radical.
Oxidation and reduction in organic chemistry.
Identify the nucleophile and electrophile in a reaction. Which compound is a better nucleophile?
Give products for these elimination reactions (E1 or E2) or substitution reaction (SN1 or SN2).
Given a molecular formula and NMR spectrum, determine the structure for a compound.
1
H NMR spectroscopy: chemical shift, integration, and the n+1 rule for splitting
Find the degree of unsaturation for a given molecular formula. Draw out isomers for that formula.
Draw out the NMR splitting pattern for the following structure.
Which systems are conjugated? Which are aromatic? (4n+2 rule)
For aromatic substitution reactions, does a substituent direct ortho/para or meta?
Which of the groups on an aromatic ring is the most powerful director?
Does a group activate or deactivate an aromatic ring? By induction or by resonance?
How would you synthesize the following di- or trisubstituted benzene?
Which compound is more acidic? Which is more basic?
Which of the carboxylic acid derivatives is the most stable? Which is the most reactive?
Preparation of carboxylic acid derivatives and their conversion to other derivatives.
Protecting groups for alcohols (TMS-Cl) and aldehyde/ketones (acetal).
Synthesis problems – know reactions needed to make an organic molecule from an alkane.
Know the following electrophilic aromatic substitution reactions.
Bromination (Br2/FeBr3)
Chlorination (Cl2/FeCl3)
HNO3/cat. H2SO4 (nitration)
Sulfonation - fuming sulfuric acid (SO3/H2SO4)
RC(=O)Cl / AlCl3 (Friedel-Crafts Acylation)
R-X / AlCl3 (Friedel-Crafts Alkylation)
Other aromatic topics
Ph-NO2
Ph-NH2 (reduction/oxidation)
Ph-CO-R
Ph-CH2-R (reduction/oxidation)
Sulfonate as a temporary blocking group
Synthesis of disubstituted aromatic compounds, ortho, meta, and para
NMR
Chemical shift regions, coupling patterns, integration, equivalent protons (skip 13C NMR)
Be able to determine a structure, using the 1H NMR spectrum and molecular formula!
Reagents for Haloalkanes (X = F, Cl, Br, I)
Cl2 or Br2 plus uv light – free radical addition to form a haloalkane
SOCl2 and PBr3 (converts R-OH to R-X for 1° and 2° alcohols)
HCl / HBr (R-OH to R-X for 3° alcohols)
NBS (for allylic bromination)
Alkene plus X2 or HX : addition to double bond (Markovnikov selectivity)
Preparation of Alcohols
Hydration of alkenes: acid-catalyzed addition of water (Markov.) or BH3/ox (Anti-Markov.)
Reduction of carbonyl compounds: NaBH4 (ald/ketones), LiAlH4 (ald/ketones/acids/esters/amides)
SN2 reaction: unhindered alkyl halide R-X reacts with OH– to form the alcohol R-OH
**Addition of Grignards or R-Li to aldehydes, ketones, and esters: mechanism, limitations
Reactions of Alcohols
Deprotonation with strong base (NH2–, K metal) to form the alkoxide RO–
Protection with Me3Si-Cl to form R-OTMS (silyl ether)
Oxidation to carbonyl: PCC or CrO3 (know when to use which reagent)
Conversion to R-X : HBr (dry, for 3° alcohols), PBr3, SOCl2 (for 1° and 2° alcohols)
Elimination to alkenes: POCl3 (1° and 2°) or H2SO4 (for 3° alcohols)
Aldehydes and Ketones
Preparation: from oxidation of primary or secondary alcohols
Addition of nucleophiles to the carbonyl carbon (Nu = H–, RLi, RMgX, CN–)
Acetal formation and use of acetals as a protecting group
Carboxylic Acids and Derivatives
Reactivity of derivatives: acid chlorides most reactive, amides least reactive
Hydrolysis of acid chlorides, anhydrides, esters, and amides to carboxylic acids
Reduction of carbox. acid derivatives with LiAlH4; addition of Grignard reagents
Preparation and reaction of carboxylic acids and their derivatives
Carbohydrates
Identify potential simple sugars. Classify as monosaccharide or disaccharide.
Cyclic hemiacetal form for sugars.
Two forms for glucose – alpha and beta
The structure and properties of starch and cellulose.
Know the following reaction mechanisms:
SN1/SN2/E1/E2 reactions: SN2/E2 transition states and SN1/E1 intermediates
Electrophilic aromatic substitution – draw out resonance structures for the cationic intermediate
Acetal formation (acid catalyzed)
Fisher esterification (acid catalyzed)
Nucleophilic acyl substitution (up-down-out) Example: acid chloride + alcohol to give ester
Synthesis of a target compound, starting from a hydrocarbon or other simple molecules.
What do PCC, CrO3, SOCl2, PBr3, NaBH4, LiAlH4, POCl3, Mg, CO2, NBS, HCl, R-Li, t-butoxide do?
Skip: 13C NMR, Wolff-Kishner, Wittig Reaction
Reaction Summaries
Substitution/Elimination
Nucleophile - strength of a nucleophile increases when:
adding a negative charge
RO- stronger than ROH
moving left on the periodic table
NH2- stronger than OHmoving down the periodic table
PH3 stronger than NH3
Bases - base strength increased by:
addition of a negative charge
RO- stronger than ROH
moving left on the periodic table
NH2- stronger than OHmoving up the periodic table
NH3 stronger than PH3
Leaving Group - good leaving groups are –OTos, –I, –Br, –Cl, and any neutral fragment (H2O)
poor leaving groups are –OH, –NH2, –OR, –CH3
Key Factors for Reaction Mechanisms
SN2 Reactions – unhindered electrophile (1°, maybe 2° R-X, but NOT 3°), good nucleophile
SN1 Reactions – stable carbocation (3°, allylic, benzylic), protic solvent (ROH or H2O), no strong base
E2 Reactions – strong base and an H next door to the leaving group; t-butoxide will promote E2
E1 Reactions - stable carbocation (3° or allylic, benzylic), protic solvent (ROH or H2O), weak base
Electrophilic Aromatic Substitution (EAS)
Directing power of various benzene substituents:
Group I (-OR, -NH2)
Group II (-X, -alkyl)
Group III (all meta directors)
Summary of Benzene Substituents
Activators:
add electron density to aromatic ring, speed up the rate of EAS, direct ortho/para
can add e- density by induction (-alkyl groups)
can add e- density by resonance (-OH, -OR, -NR2, -Ph )
Deactivators: remove electron density from aromatic ring, reduce rate of EAS, direct meta
can remove e- density by induction (-CF3, -N+R3, -SO3H, -NO2 )
can remove e- density by resonance (-NO2, -CN, -C(=O)-R carbonyl)
Halogens: deactivators that are ortho/para directors
Synthesis Tips
Count carbons, and check the carbon skeleton. What carbon atoms must be added?
To add carbons to a molecule, use Grignard plus carbonyl (most of the time).
Starting w/ an alkane, free radical halogenation (X2/uv light) is the only option.
To make an alkane, use catalytic hydrogenation of an alkene (H2/cat).
Aldehydes and ketones are formed by oxidation of the corresponding alcohol.
Use an alkene to get TWO carbons involved in a functional group.
Convert between alcohols and alkyl halides using the proper reagent.