Organic Reactions in Detail

Organic Reactions in Detail

I.

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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)

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

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

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

The presence of the triple bond makes these very reactive.

4. / Aromatic / hydrocarbons-all involve the molecule benzene C6H6.

Aromatic compounds are very stable. The double bonds in benzene are delocalized (creates resonance). Benzene molecules are very carcinogenic.

ortho-dichloro benzene / / meta-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).
/ +Br2 / / / +HBr
B. / Addition: characteristic of double bond (alkenes).
/ +Br2 / /

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.

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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

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).
/ +O2 / /
Oxidizing a hydrocarbon gives an alcohol.
b. / Can be formed by reduction (addition of hydrogen, removal of oxygen, or both)
/ +H2 / /

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)
General formula R-O-R'
Diethyl ether-anesthetic, good solvent. Vapors highly flammable.
3. / Aldehydes / have carbonyl group () bonded to at least one hydrogen atom. Add the suffix -al.
formaldehyde / acetaldehyde / propionaldehyde
methanal / ethanal / propanal

General formula:

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 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.
/ +O2 / / / +H2O
2-propanol + / oxygen / / 2-propanone
acetone
dimethyl ketone / +water

General formula:

5. / Acids / contain a carboxyl group, ,general form, , suffix is an -ioc ending.
/ + O2 / / / + 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

Organic acids ionize by:

/ / / + 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.
/ + / / / / +H2O
acetic acid / + / methanol / / methyl acetate** / +water

**Note: the alcohol residue comes first, then the acid.
-Most esters have a very pleasant odor.

/ + / / / / +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
B. / Amides / have a carbonyl group and an amine (pronounced a-mids). Add -amide suffix.
C. / AminoAcids / are organic acids with a amine group directly next to the carboxyl group.
D. / Nitro / are a NO2 group. Nitro- prefix.
E. / Nitrile / a carbon triple bonded to a nitrogen. Add -nitrile suffix.

III.

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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.

/ +3NaOH / / / + / 3
fat / +sodium hydroxide / / glycerol / + / 3soap

Soap cleans because:

a. / Long chain hydrocarbon has a good solvent action on other hydrocarbons.
b. / end 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
/ + / / / / + H2O
salicylic acid / + / acetic acid / / acetyl salicylic acid
(aspirin) / +water
3. / AcidAnhydrides / -a compound formed when two carboxyl groups join releasing a water.
/ + / / / H2O+ /