G11 Chemistry, LC4, Section 18.2 notes
Section 18.2: Substituted Hydrocarbons
Functional Groups:
-Substituted hydrocarbons: compounds are the same as hydrocarbons except for the substitution of
atoms of another element for part of the hydrocarbon.
-Functional group: The part of a molecule having a specific arrangement of atoms that is largely
responsible for the chemical behavior of the parent molecule. Functional groups can be atoms, groups of
atoms, or bond arrangements.
- Replacing part of a hydrocarbon with functional groups changes the structure, properties, and uses that
we have for the compounds
- Double and triple bonds also are considered to be functional groups.
Functional Groups: Structure and Function:
1- Halogenated Compounds:
structure: R—X , where X = F, Cl, Br, or I
functional group: halogen atoms
properties: high density
uses: refrigerants, solvents, pesticides, moth repellents, some plastics
biological functions: thyroid hormones
examples: chloroform, dichloromethane, thyroxin, Freon,
DDT, PCBs, PVC
2- Alcohols
structure: R—O—H
functional group: hydroxyl group (—OH); hydrogen atom bonded to an oxygen atom, which is bonded to the hydrocarbon
part of the molecule
properties: polar, so water molecules are attracted to it; high boiling point; alcohols with low molecular weights are
water-soluble
uses: solvents, disinfectants, mouthwash and hair-spray ingredient, antifreeze
biological functions: reactive groups in carbohydrates, product of fermentation
examples: methanol, ethanol, isopropanol (one type of rubbing alcohol), cholesterol, sugars
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3- Carboxylic Acids:
functional group: carboxyl group (—COOH); oxygen atom double bonded to a carbon, which is also bonded to a hydroxyl
group and the hydrocarbon part of the molecule
properties: acidic, usually water-soluble, strong unpleasant odors, form metal salts in acid-base reactions
uses: vinegar, tart flavoring, skin-care products, production of soaps and detergents
biological functions: pheromones, antsting toxin; causes rancid-butter and smelly-feet odors
examples: acetic acid (in vinegar), formic acid, citric acid (in lemons), salicylic acid
4- Esters:
derived from carboxylic acids in which the —OH of the carboxyl group has been replaced with an —OR from an alcohol
properties: strong aromas, volatile
uses: artificial flavorings and fragrances, polyester fabric
biological functions: fat storage in cells, DNA phosphate-sugar backbone, natural flavors and fragrances, beeswax
examples: banana oil, oil of wintergreen, triglycerides (fats)
5- Ethers:
structure: R—O—R’ ; oxygen atom bonded to two hydrocarbon groups
properties: mostly unreactive, insoluble in water, volatile
uses: anesthetics, solvents for fats and waxes
examples: diethyl ether
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6- Ketones and Aldehydes:
functional group: carbonyl group (—CO); carbon atom double bonded to an oxygen atom
properties: very reactive, distinctive odors
uses: solvents, flavorings, manufacture of plastics and adhesives, embalming agent
examples: acetone; formaldehyde; cinnamon, vanilla, and almond flavorings
Acetone
7- Amines and Amides:
functional group: amine: amino group (—NH2); two hydrogen atoms bonded to a nitrogen atom, which is bonded to the
hydrocarbon part of the molecule
amide: amino group bonded to a carbonyl group (—CONH2)
properties: amines: basic, ammonia-like odor
amides: neutral, most are solids
uses: solvents, synthetic peptide hormones, fertilizer, nylon synthesis
biological functions: in amino acids, peptide hormones, and proteins; distinctive odor of some cheeses
examples: urea, putrescine, cadaverine, Nutrasweet
Where do all the alcohols needed by industry come from?
1- Cracking process is used to synthesize ethanol, the two-carbon compound that contains an alcohol
functional group.
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2- Fermentation; when yeast cells ferment the sugars and starches in plant materials.
Important questions:
1. Explain why organic compounds with similar structures often have similar uses.
Uses depend on properties, which depend on structures.
2. Distinguish between an aldehyde and a ketone.
Ketones have a carbonyl group bonded between two hydrocarbon groups. In an aldehyde, one of the hydrocarbon groups is
replaced by a hydrogen atom.
3. Circle and name each type of functional group present.
one hydroxyl group, four halogen (I) atoms, one ether group, one amino group, one carboxyl group, two benzene rings
4- Draw the structure of an ether, where R is —CH3 and R’ is —CH2CH3.
CH3—O—CH2CH3
5- Water is released in a reaction in which two different functional groups condense to form an ester. What two functional
groups take part in this reaction?
Hydroxl groups and carboxylic acid condense to form esters.
6- Glycerol and isopropanol are both alcohols. Each contains a three-carbon chain, but glycerol has three alcohol functional
groups, whereas isopropanol has only one. Predict which alcohol will be more soluble in water.
Glycerol will be more soluble in water than isopropanol because it can form more hydrogen bonds.
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