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Organic Chemistry Functional Groups
• The hydrocarbon skeleton of an organic molecule is chemically inert. • Most organic chemistry, then, involves the atoms and molecules that are attached to this main chain.
• Functional groups are the atoms in an organic compound that have been added to a hydrocarbon chain. They are the only part of the molecule that is capable of reacting chemically.
• Compounds are classified according to their functional groups. Since these groups can be attached to any chain, we will represent the inert hydrocarbon chain with “R”.
• The presence of a functional group has a major effect on the physical properties of a compound. • Intermolecular forces determine many physical properties, such as solubility and boiling point: • hydrocarbons – have only weak dispersion forces. • functional groups – may have strong hydrogen bonds.
Hydrogen Bonding • Boiling Points: Compounds with hydrogen bonding have higher than expected boiling points: at SATP, C2H6 = gas but CH3OH = liquid. • Solubilities: Compounds with hydrogen bonds are usually soluble in water (a polar molecule): C6H14 = insoluble in water but C5H11OH = soluble in water. • Solubility decreases, as the molecule gets longer. (C12H25OH =slightly soluble in water). – This is because the hydrogen bonding –OH group has less effect on the larger molecule.
Halocarbons • Halocarbons are produced by the substitution of a halogen (Family VIIA) for hydrogen in the hydrocarbon chain Cl = chloro Br = bromo I = Iodo F = Fluoro NO2 = nitro NH2 = amino
• The halocarbon is treated as a substituent. • Don’t forget that substituents are named alphabetically. • CH3-C(Br)(CH3)-CH3 2-bromo-2-methylpropane • CH3-CH(Cl)-C(NO2)(C2H5)-CH2-CH3 2-chloro-3-ethyl-3-nitropentane
Practice • Name or provide the formula for the following: a) CH3-CH2(I) b) CH2(Cl)-CH2(Cl) c) CH(F)(F)-CH(Cl)(Cl) d) CH3-CH2-CC-CH2(NH2) e) CH3-CH(NO2)-CH2(Br)
f) trichloromethane g) 2-chloro-3-iodo-1-butene h) 1,5-dinitro-2-pentyne i) 1,3-difluorocyclopentane j) 1,3-dibromo-3-phenylhexane
Alcohols • Alcohols contain the hydroxyl (-OH) group: R–O–H • Nomenclature: Add “-ol” to the stem of the name of the parent chain. Number the position of the hydroxyl group. • If more than one –OH group is present, use these endings: a)“-diol” (two hydroxyls) b) “-triol” (three hydroxyls)
Examples • CH3-CH(OH)-CH3 2-propanol • CH3-CH(CH3)-CH2-CH2(OH) 3-methyl-1-butanol • CH2(OH)-CH2-CH(OH)-CH3 1,3-butandiol
• Phenols are alcohols in which the –OH group is attached to benzene.
• Name or give the formulas for the following: a) CH3-CH(OH)-CH3 e) 2-pentanol b) CH2(Cl)-CH(OH)-CH3 c) CH2(OH)-CH(OH)-CH2-CH3 d) C6H4(OH)(CH3)
f) 2,2,4-pentatriol g) 3-ethyl-2-pentanol h) 2-ethylphenol
Properties • Alcohols tend to have high boiling points due to the strong hydrogen bonding that occurs between these molecules. • Smaller molecules are also soluble in water as they can hydrogen bond with the polar water molecules. • Longer chain molecules tend to be insoluble as the hydroxyl group has less effect on the molecule. They can be good solvents for non-polar molecular compounds (“like dissolves like”).
Ethers • These are compound in which oxygen is bonded between two carbon groups.
• The two-alkyl groups are named in alphabetical order and followed by the word “ether”. CH3-CH2-CH2-O-CH3 CH3-CH2-O-CH2-CH3 methylpropyl ether diethyl ether
Aldehydes and Ketones • These two families share certain structural features and chemical properties. • They both contain the carbonyl group which we will show as (-C(=O)-) in our condensed formulas.
• Aldehydes = chain + carbonyl group + hydrogen
• Ketones = chain 1 + carbonyl group + chain 2
Naming • Aldehydes: change the “_e” ending to “_al”
propanal
• Ketones: count the total number of carbons present. Change the “_e” ending to “_one”. Number the carbonyl location.
propanone
3-hexanone
• Properties: - They have low boiling points because they have no O – H bonds for hydrogen bonding. • -When added to water, though, they can hydrogen bond to the water molecules so they are quite soluble in water.
Try This • Draw and name the aldehyde and the ketone with the molecular formula of C4H8O. • AW p. 628, Name: CH3CH2CHO CH3-CH2- CH(CH3)-CH2-CHO CH3-CH2-CH2-C(=O)-CH2-CH3 CH3-C(=O)-CH2-CH3
Carboxylic Acid • These organic acids contain the carboxyl functional group, -C(=O)-OH which include both the carbonyl group and the hydroxyl group. In molecular formulas, the carboxyl group is often presented as –COOH.
• Carboxylic acids create the sour taste in foods and have distinctive odors. • They are polar molecules and are both hydrogen acceptors and hydrogen donors. Thus they will readily form hydrogen bonds, and smaller molecules are easily dissolved in water. • They have all of the properties of acids – react with metals, make indicators change color, etc.
Naming •
Replace the “_e” ending with “_oic acid”.
Propanoic acid
• • • • • • •
Name a) CH3-CH2-CH2-C(=O)OH b) CH3-C(CH3)(CH3)-C(=O)OH c) COOH Give the formula for a) hexanoic acid b) 3-methylpentanoic acid
Ester • Esters are derivatives of carboxylic acids in which the – OH of the carboxyl group has been replaced by an – OR from an alcohol.
Naming • • •
The name of an ester has two parts: Locate the alcohol branch and name it as an alkyl group. Locate the acid branch. The ending of the acid name is changed from “_oic acid” to “_oate”
ethyl propanoate
methyl ethanoate
Properties • Esters are “odor” chemicals (fruits and flowers). • are added to foods to enhance taste + odor.
Try This • P. 411 McGraw Hill a b
c
Draw these • • • • •
methyl pentanoate heptyl methanoate butyl ethanoate propyl octanoate ethyl 3,3-dimethylbutanoate
Amines and Amides • There are two functional groups which contain nitrogen atoms connected to carbons: the amines and the amides.
amine
amide
• Amines and amides are abundant in nature. They are a major component of proteins and enzymes and nucleic acids • Many are toxic • Amines with low molecular masses smell like fish • Many smells of decay are caused by amines
Amines • Amines are organic derivatives of ammonia, NH3, in which one or more of the three H’s is replaced by a carbon group • Amines are classified as primary (1°), secondary (2°), or tertiary (3°), depending on how many carbon groups are connected to the nitrogen atom.
Naming • Identify the largest hydrocarbon group attached to the N atom as the parent alkane. • Replace the –e at the end with the new ending – amine. Include a position number, if necessary, to show the location of the functional group on the hydrocarbon chain • Name the other alkyl group(s) attached to the N atom. Use the letter N- to locate the group(s). If there are two, you will use N,N. This is the prefix. • Put together prefix + root + suffix
3 – hexanamine There is a chain of 6 carbons and the N group is located at the third C.
N-ethyl-N-methyl-2-propanamine
The propyl group is the largest group. So propane is the parent alkane. The N atom is found off of the second C A methyl group is attached to the N atom.
An ethyl group is attached to the N atom
Practice • Name each amine: a) CH3-NH2 b) CH3CH2CH(CH3)NH2 c)
d)
e)
f)
• Other examples: • http://www.muhlenberg.edu/depts/chemistr y/chem201woh/opa091203a.htm
Properties • Tend to be polar • Hydrogen bonding takes place • Solubility decreases as the number of carbon atoms increases • Boiling points of primary and secondary amines are higher than boiling points of tertiary amines
Amides • Has a carbon atom double-bonded to an oxygen atom and single-bonded to an nitrogen atom
Naming •Locate the part of the amide that contains the C=O group. Name the parent carboxylic acid from which this part is derived. This is always position one. •Replace the –oic acid with –amide •Decisions: •If there are two hydrogen atoms attached to the N atom, there are no other prefixes •If there is one alkyl group attached, name the alkyl group and give it location letter N •If there are two alkyl groups, place them in alphabetical order. N must be used. If the groups are identical, use N,N •So: prefix + root + prefix
Examples Methanamide
One alkyl group, one carbon One alkyl group, two carbons ethanamide
N-methylpropanamide
There are two alkyl groups, a methyl and a propyl
propyl
• 2-methylpropanoic acid is the parent acid • So the base name is 2-methylpropanamide • A propyl group is attached to the N
N-propyl-2-methylpropanamide
Properties • N atoms attracts electrons more strongly than C or H, so it is polar • Hydrogen bonding (N-H) • Soluble in water • Many are solid at room temperature
• • • • •
Examples: acetaminophen Urea Valium Thalidomide
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