Organic Chemistry Chapter 22

Organic Chemistry The study of carbon-containing compounds and their properties. The vast majority of organic compounds contain chains or rings of carbon atoms.

Organic & Inorganic Compounds Originally the distinction between inorganic and organic substances was based on whether or not they were produced by living systems. In 1828, German chemist Friedrich Wohler prepared urea from the inorganic salt ammonium cyanate by simple heating: heat NH4OCN ---> NH2CONH2

Hydrocarbons . . . compounds composed of carbon and hydrogen. Saturated: carbon-carbon bonds are all single - alkanes [CnH2n+2]

Hydrocarbons (continued) Unsaturated: contains carbon-carbon multiple bonds.

C2H4(g) + H2(g) ---> C2H6(g) Hydrogen Addition C2H4(g) + H2(g) ---> C2H6(g) unsaturated saturated

The carbon-hydrogen bonds in methane.

The Lewis structure, space-filling, and ball- and-stick models for ethane.

The structures of propane and butane with 109.5o bond angles.

Structural Isomerism -- isomers contain the same atoms but one or more different bonds.

Normal butane (n-butane) and the branched isomer, isobutane.

Isomers of Pentane What are the three isomers of pentane? 1) n-pentane -- straight-chain 2) isopentane -- one branch from 2nd carbon 3) neopentane -- two branches from central carbon

The straight-chain isomer, n-pentane.

Rules for Naming Alkanes 1. For alkanes beyond butane, add -ane to the Greek root for the number of carbons. C-C-C-C-C-C = hexane 2. Alkyl substituents: drop the -ane and add -yl. -C2H5 is ethyl

Rules for Naming Alkanes 3. Positions of substituent groups are specified by numbering the longest chain sequentially. C  C-C-C-C-C-C 3-methylhexane 4. Location and name are followed by root alkane name. Substituents in alphabetical order and use di-, tri-, etc. See Sample Exercise 22.2 on pages 1062-1064.

Combustion Reactions of Alkanes C3H8(g) + 5O2(g) ----> 3CO2(g) + 4HOH(g) 2C4H10(g) + 13 O2(g) ----> 8CO2(g) + 10HOH(g)

Substitution Reactions for Alkanes Primarily where halogen atoms replace hydrogen atoms.

Dehydrogenation Reactions Cr2O3 CH3CH3 ----> CH2=CH2 + H2 500oC ethane ethylene

Cyclic Alkanes Carbon atoms can form rings containing only carbon-carbon single bonds. C3H6, C4H8, C6H12 Shorthand notation for the cyclic alkanes.

The molecular structure of cyclopropane and the overlap of the sp3 orbitals that form the C-C bonds.

The chair and boat forms of cyclohexane.

Alkenes and Alkynes Alkenes: hydrocarbons that contain a carbon- carbon double bond. [CnH2n] CC=C propene Alkynes: hydrocarbons containing a carbon- carbon triple bond. [CnH2n-2] CCCCC 2-pentyne

Nomenclature for Alkenes 1. Root hydrocarbon name ends in -ene C2H4 is ethene 2. With more than 3 carbons, double bond is indicated by the lowest numbered carbon atom in the bond. C=CCC is 1-butene

The bonding in ethylene.

The two stereoisomers of 2-butene. a) cis-2-butene b) trans-2-butene

The bonding in ethane allows rotation and no cis-trans isomerism.

The bonding in acetylene.

Addition Reactions . . . in which (weaker)  bonds are broken and new (stronger)  bonds are formed to atoms being added. propene propane

Halogenation CH2=CHCH2CH2CH3 + Br2 ---> CH2BrCHBrCH2CH2CH3 1-pentene 1,2-dibromopentane

Aromatic Hydrocarbons A special class of cyclic unsaturated hydrocarbons. + Cl2 + HCl benzene Chlorobenzene

Aromatic Hydrocarbons phenyl group Ortho (o-) -- two adjacent substituents. meta (m-) -- two substituents with one carbon between them. para (p-) -- two substituents opposite each other.

Refinery Processes Cracking: large molecules broken down to smaller ones by breaking carbon-carbon bonds. Pyrolysis (thermal cracking): The process that produces cracking at high temperatures. Catalytic Cracking: Cracking at lower temperatures. Catalytic reforming: Alkanes and cycloalkanes converted to aromatic compounds.

The Common Functional Groups Class General Formula Halohydrocarbons RX Alcohols ROH Ethers ROR Aldehydes

The Common Functional Groups Class General Formula Ketones Carboxylic Acids Esters Amines RNH2 Amides R-C=ONH2

Alcohols contain the hydroxyl group (-OH).

Aldehydes & Ketones contain the carbonyl group ( C=O ). In ketones the carbonyl group is bonded to two carbon atoms -- CH3C=OCH3. In aldehydes the carbonyl group is bonded to at least one hydrogen atom -- HCHO.

Carboxylic Acids & Esters Carboxylic acids contain the carboxyl group O (-C-OH). Esters contain the -C-O- group.

Amines & Ethers Amines contain -NH2 group. If one hydrogen is removed and replaced with a hydrocarbon group, it is a primary amine. If two hydrogen are replaced, it is a secondary amine. If all three hydrogens are replaced, it is a tertiary amine. Ethers contain the -O- group.

Polymers . . . are large, usually chainlike molecules that are built from small molecules called monomers. Monomer Polymer Ethylene Polyethylene Vinyl chloride Polyvinyl chloride Tetrafluoroethylene Teflon

Types of Polymerization Addition Polymerization: monomers “add together” to form the polymer, with no other products. (Teflon) Condensation Polymerization: A small molecule, such as water, is formed for each extension of the polymer chain. (Nylon)