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) f) trichloromethane b) CH2(Cl)-CH2(Cl) g) 2-chloro-3-iodo-1-butene c) CH(F)(F)-CH(Cl)(Cl) h) 1,5-dinitro-2-pentyne d) CH3-CH2-CC-CH2(NH2) i) 1,3-difluorocyclopentane e) CH3-CH(NO2)-CH2(Br) 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
Name or give the formulas for the following: a) CH3-CH(OH)-CH3 e) 2-pentanol b) CH2(Cl)-CH(OH)-CH3 f) 2,2,4-pentatriol c) CH2(OH)-CH(OH)-CH2-CH3 g) 3-ethyl-2-pentanol d) C6H4(OH)(CH3) 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. 3-hexanone propanone
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” methyl ethanoate ethyl propanoate
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-dimentylbutanoate
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: CH3-NH2 CH3CH2CH(CH3)NH2 e) c) f) d)
Other examples: http://www.muhlenberg.edu/depts/chemistry/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 oxygen 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 N-propyl-2-methylpropanamide 2-methylpropanoic acid is the parent acid So the base name is 2-methylpropanamide A propyl group is attached to the N
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