Organic Chemistry Chapter 25 Chemistry 100
Organic Chemistry • Historically: the chemistry of products from plants and animals • Today: The chemistry of carbon- containing compounds • Wöhler (1828) made urea from ammonium cyanate • Distinction between “natural” and “synthetic” chemicals disappeared.
The world of plenty • The American Chemical Society has a database with more than 11 million organic compounds • Why so many? • Because carbon can make chains and rings, and things
Carbon • Electronic configuration 1s22s22p2 • Needs 4 electrons to complete the shell • Electronegativity 2.5 so it forms covalent bonds with other elements • 2s22p2 makes hybrid orbitalssp3 - tetrahedron
Functional Groups • We look at an organic molecule and ask “what functional groups does it have? • Examples • Alcohols have the OH group • Amines have the NH2 group • Unsaturated compounds have double or triple bonds C=C or CC
Functional groups • Acetic acid CH3COOH is a carboxylic acid - it has the -COOH group • The compound CH3NH2 is methyl amine • An amino acid like glycine (see picture) has both the carboxylate and the amino group
Categorizing organic compounds • There are so many we need a system to name them • Unlike biologists we use English words, but sometimes you would not know this!
Hydrocarbonscontain only C and H • Aliphatic (meaning derived from fats) • Alkanes CnH2n+2 • Alkenes CnH2n • Alkynes CnH2n-2 • Aromatic (yes - they smell) contain one or more benzene rings
Alkanes CnH2n+2 • n = 1 Methane (marsh gas) CH4 • n = 2 Ethane C2H6 • n = 3 Propane C3H8 • n = 4 Butane C4H10 • n = 5 Pentane (liquid) C5H12 • n = 6 Hexane C6H14 • n = 7 Heptane C7H16 • n = 8 Octane C8H18 • n = 9 Nonane C9H20 • n = 10 Decane C10H22
Butane Condensed formula (two forms) Lewis structural formula
Iso-butane A branched chain We may think of this as CH3CH2CH3 with one of the H atoms substituted by a CH3 group
Alkylgroups CH3Cl methyl chloride CH3CH2CH2OH n-propyl alcohol
Naming larger alkanes • Find the longest continuous chain. Use this as the base name • Number the C atoms, starting from the nearest substitution • Name and give location of each substitued group • When more than one group at the same location: use di, tri, tetra, penta if they are the same name in alphabetical order, if different
Cycloalkanes CnH2n Cyclopropane cyclobutane cyclopentane cyclohexane
Reactions of alkanes • Combustion • Substitution reactions C2H6 + Cl2 C2H5Cl + HCl
Unsaturated hydrocarbons • alkenes CnH2n contain a double bond ethylene or ethene C2H4 propylene or propene C3H6 • alkynes CnH2n-2 contain a triple bond acetylene C2H2 propyne C3H4
C H C H 3 3 2-methyl-2-butene H C H 3 H C C H C H 3 2 3 2-pentene H H C H C H = C H 3 2 Sample alkenes
Alcohols; R-OH • The hydroxyl or alcohol functional group -OH • The OH group is polar; hydrogen bonding makes alcohols more soluble in water than in hydrocarbons • CH3OH methyl alcohol, methanol, “wood alcohol”. Impurity in moonshine; causes blindness • CH3CH2OH ethyl alcohol, ethanol, “alcohol” Prepared by fermentation of sugar-containing plant material.
Reactions with alcohols • The OH group does NOT make alcohols basic. In fact, phenol is weakly acidic. • An important reaction is esterification - the formation of esters when an alcohol reacts with an acid. See notes on carboxylic acids
Ethers R-O-R • The -O- bridge • CH3CH2-O-CH2CH3 is diethyl ether, or “ether”. Used in medicine but not as much as at one time. Very explosive! • Ethers are used industrially as solvents
Aldehydes • Some aldehydes have common names like formaldehyde and acetyaldehyde. • The other way to name them is with the al ending. CH3CH2CHO is propanal or propyl aldehyde
Esters • Carboxylic acid + alcohol ester + water • For organic chemists, reactions that generate water are called condensation reactions • The condensation reaction is called esterification • Fruity smell. Pentyl acetate (amyl acetate) gives bananas their smell but is very poisonous in large amounts.
Hydrolysis of ester • Ester + water carboxylic acid + alcohol • The reverse of esterification • When done using a base (NaOH, for example), the reaction is called saponification. • Soap was made by reacting fat (esters of stearic acid and glycerin) with NaOH to get sodium stearate.
Amines R-NH2 , R2NH, R3N • Organic chemistry’s base. • Think of amines as substituted ammonia NH3 + R RNH2 R2NH R3N • Just as NH3 is an proton acceptor making NH4+ , so amines are proton acceptors. • They also react with carboxylic acids to give amides • Horrid smell. One is called putricine, another cadaverine
Amino acids • A compound with the carboxylic acid group and the amine group
Peptides &Proteins • The amine group of one acid reacts with the carboxylic acid group of another to make a peptide • When more molecules add on, we get a polypeptide • Certain polypeptides are of biological importance - proteins
Carbohydrates • Have the general formula Cn(H2O)n • The simple sugars glucose and fructose are the basic building units of many carbohydrates. These sugar molecules can make rings. • Disaccharides like table sugar (sucrose) consists of two rings joined together. • When many rings join we get starch or cellulose. The difference is in how the rings are joined. We can digest starch but not cellulose