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AP Chemistry

Organic Chemistry Notes

(Chapter 22 )


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All organic chemistry is based upon unique properties of the carbon atom.
Carbon, C, hybridization to 3 sp3 orbitals, carbon can now form 4 bonds, may be single, or in combination of double (sp2) or triple bonds (sp). Carbon forms very strong bonds with many non-metal atoms, H, O, Cl, N.
Note: silicon and germanium are in the same family and form 4 bonds, but the bond energy is low, so weak bonds are formed. This severely restricts their chemistry.

I.

Hydrocarbons

4 categories: alkanes, alkenes, alkynes, and aromatic compounds

1. Alkanes:  carbon atoms are bonded to each other with single bonds. Each C has 4 bonds (sp3 hybrid). Bonds are directed to corners of a tetrahedron (bond angles of 109.5o). Chains are "zig-zag". The general rule for writing formulas is 2n+2. Where n represents the number of carbons and 2n+2 equals the number of hydrogens.

methane (1C), ethane (2C's), propane (3C's), butane (4C's), pentane (5C's), hexane (6C's), heptane (7C's), octane (8C's), nonane(9C's), decane(10C's)

Isomerization- same molecular formula, but different structure. Also creates different properties for the molecule. The number of possible isomers increases rapidly as the length of the chain increases.

n-butane 2-methyl propane (iso-butane)
n-butane 2-methyl propane

**When adding carbon "groups" to the main chain, add the ending yl. e.g. methyl, ethyl, propyl, butyl. These are called substituents.

n-hexane n-hexane 2n+2
2(6)+2=14
Therefore it is C6H14
2-methyl pentane 2-methyl pentane
3-methyl pentane 3-methyl pentane
2,3-dimethylbutane 2,3-dimethyl butane
2,2-dimethyl butane (not 3,3-dimethyl butane) 2,2-dimethyl butane

Alkanes, straight or branched chains, all have an exterior which is mostly hydrogen atoms. Surface of one molecule is quite like any other. No well-defined + or - center, so they are non-polar. Soluble in each other and in other non-polar solvents. (not soluble in water, which is very polar).

Alkanes are rather unreactive chemically. Principle reaction is burning in air (combustion reaction). Also are involved in substitution reactions.

Cycloalkanes: molecular formula has 2 less H atoms than straight chain (2n).
cyclohexane cyclobutane cyclopropane
cyclohexane cyclobutane cyclopropane
2. Alkenes  (unsaturated hydrocarbon, olefin) contains one double bond. Made by cracking an alkane (heating long-chain alkane in presence of catalyst). This causes (among other things) a double bond to form, and the elimination of two H's. General rule: 2n, creates at least one pi bond. Has sp2 hybridization on the double bond.

No rotation about the double bond, this leads to the formation of geometric isomers.
cis-2-butene trans-2-butene
cis-2-butene trans-2-butene
The presence of the double bond makes alkenes more reactive than alkanes. Also can polymerize.

3. Alkynes  contain 1 triple bond. General rule, 2n-2, sp hybridization around the triple bond.

acetylene
ethyne
1-butyne
ethyne 1-butyne
The presence of the triple bond makes these very reactive.
4. Aromatic  hydrocarbons-all involve the molecule benzene C6H6.
benzene representation 1 benzene representation 2 benzene representation 3
Aromatic compounds are very stable. The double bonds in benzene are delocalized (creates resonance). Benzene molecules are very carcinogenic.
ortho-dichloro benzene
ortho-dichloro-benzene
meta-dichloro benzene
meta-dichloro benzene
para-dichloro benzene
para-dichloro benzene
note: each benzene still has H's at each C without a chlorine

5. Types of Reactions of Alkanes and Alkenes
A. Substitution: characteristic of single bonds (alkanes).

ethane + Br2 -U.V. Light-> 1-bromo ethane + HBr

B. Addition: characteristic of double bond (alkenes).
ethene + Br2 --> 1,2-dibromo ethane
Note: no byproduct.
Addition reactions are a good test for a double bond. A diatomic bromine solution of carbon tetrachloride is reacted with the suspected compound. If a double bond is present, red color (from Br2) will quickly fade.

II.

Hydrocarbon Derivatives

1. Alcohols  contain the hydroxide group, OH, substituted for hydrogen. Suffix is -ol.
methyl alcohol ethyl alcohol propyl alcohol isopropyl alcohol
methanol ethanol propanol 2-propanol
methanol ethanol propanol 2-propanol

General formula R-OH, where R is an alkyl group. Hydrogen bonding in the -OH group causes alcohols to have a high boiling point.
a. Can be formed by oxidation (addition of oxygen, removal of H on both).
methane +O2 --> methanol
Oxidizing a hydrocarbon gives an alcohol.

b. Can be formed by reduction (addition of hydrogen, removal of oxygen, or both)
methanal +H2 --> methanol
This process is used for about 80% of industrial ethanol production.
Methanol-present in liquid distillate from heating wood and oxygen, "wood alcohol", deadly and causes blinding.
2. Ethers -oxygen singly bonded to two carbon atoms.
dimethyl ether ethyl methyl ether diethyl ether (anesthetic)
dimethyl ether ethyl methyl ether diethyl ether
General formula R-O-R'
Diethyl ether-anesthetic, good solvent. Vapors highly flammable.

3. Aldehydes have carbonyl group (-C=O) bonded to at least one hydrogen atom. Add the suffix -al.
formaldehyde acetaldehyde propionaldehyde
methanal ethanal propanal
methanal ethanal propanal
General formula: aldehyde

The boiling point for aldehydes is lower than the corresponding alcohol's, since there is no hydrogen bonding. The boiling point is much higher than corresponding saturated hydrocarbons, since -C=O bond is highly polar.

Produced by oxidizing an alcohol with a terminal -OH group. Reduction is the oppsite process.

4. Ketones  have a carbonyl on the interior of the chain. Oxidation of an alcohol with non-terminal -OH. Suffix is an -one ending.
2-propanol 1/2O2 --> propanone + H2O
2-propanol + oxygen --> 2-propanone
acetone
dimethyl ketone
+ water
General formula: ketone

5. Acids  contain a carboxyl group, carboxyl group,general form, acid group, suffix is an -ioc ending.
ethanol + O2 --> ethanoic acid + H2O
ethanol + oxygen --> acetic acid
(vinegar)
+ water

formic acid propionic acid butyric acid
from "formica" (ants) acetic acid (rancid butter)
methanoic acid ethanoic acid propanioc acid
methanoic acid ethanoic acid propanoic acid
Organic acids ionize by:
acid --> acid anion + H+
-Most are weak acids.
-As the length of the chain increases, organic acids become less soluble in water and more soluble in non-polar solvents (remember that the -OH creates high polarity).

6. Esters  are produced by a reaction between an acid and an alcohol.
ethanoic acid + methanol --> methyl acetate + H2O
acetic acid + methanol --> methyl acetate** + water
**Note: the alcohol residue comes first, then the acid.
-Most esters have a very pleasant odor.
salicylic acid + methyl alcohol --> methyl salicylate + H2O
salicylic acid + methyl alcohol --> methyl salicylate
(wintergreen)
+ water

7. Nitrogen Functional Groups
A. Amines  are derivatives of ammonia in which one or more N-H bonds have been replaced with a N-C bond. The name amine represents the -NH2 functional group.
Primary amine Secondary amine Tertiary amine
primary amine secondary amine tertiary amine
B. Amides  have a carbonyl group and an amine (pronounced a-mids). Add -amide suffix.
amide
C. Amino Acids  are organic acids with a amine group directly next to the carboxyl group.
amino acid
D. Nitro  are a NO2 group. Nitro- prefix.
nitro group
E. Nitrile  a carbon triple bonded to a nitrogen. Add -nitrile suffix.
nitrile group

III.

Miscellaneous

1. Soaps
Animal and vegetable fats are esters made of
a. Long-chain organic acids (fatty acids)
b. Various alcohols, glycerol (glycerin) is the most common. Glycerol is a triol.

Reacting a fat with NaOH splits the fat into glycerin and the sodium salt of the fatty acid. This sodium salt is the soap.
fat + 3 NaOH --> glycerol + soap
fat + sodium hydroxide --> glycerol + 3 soap
Soap cleans because:
a. Long chain hydrocarbon has a good solvent action on other hydrocarbons.
b. soap anionend has a high water solubility.

Soaps from 'scum" in hard water. "Scum" is a precipitates of the Ca2+ and Mg2+ of the soap. Detergents contain poly phosphorus ions, which tie up the Ca2+ and Mg2+ ions so the detergent can do its work.

2.Aspirin
salicylic acid + ethanoic acid --> aspirin + H2O
salicylic acid + acetic acid --> acetyl salicylic acid
(aspirin)
+ water
3. Acid Anhydrides -a compound formed when two carboxyl groups join releasing a water.
acid group + acid group --> H2O + acid anhydride


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