CHAPTER 8INTRODUCTION TO ORGANIC CHEMISTRY BASIC CHEMISTRY CHM 138
ORGANIC CHEMISTRY • Organic chemistry: • The branch of chemistry that deals with carbons compounds. • ‘Organic’ – derived from living organisms • Study of compounds extracted from living organisms and their natural products. • Examples: sugar, starch, urea, waxes, carbohydrates, fats and etc • Human are composed of organic molecules – proteins in skin, lipid in cell membranes, glycogen in livers and the DNA in the nuclei of cells.
Chemistry of carbon: - Two stable isotops (13C and 12C) - electron configuration: 1s2 2s2 2p2 - four valence electrons - can form more compounds than any other element - able to form single, double and triple carbon-carbon bonds, and to link up with each other in chains and ring structures
HOMOLOGUE SERIES AND FUNCTIONAL GROUPS • Functional group: A group of atoms that is largely responsible for the chemical behavior of the parent molecule. • Functional groups: - hydrocarbons - alcohols - aldehydes - ketones - carboxylic acids - alkyl halides
HYDROCARBONS • Made up of only hydrogen and carbon
ALKANES • General formula: CnH2n+2, where n = 1, 2, …. • Only single covalent bonds are present • Known as saturated hydrocarbons because contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms present. • Can be assumed to be sp3-hydridized
The melting and boiling points of the straight-chain isomers of the first 10 alkanes
Homologous Series • Definition: A series of compounds in which each member differs from the next by a specific number and kind of atoms. • Alkanes: Differ only at number of (CH2) • Series of compounds that has the same functional group.
NAMING ALKANES • Alkyl groups are used to name organic compounds. • The general formula of an alkyl group is CnH2n+1. • The letter “R” is often used in formulas to represent any of the possible alkyl groups. R= CnH2n+1 (any alkyl group) R = CH3 — methyl group R = CH3CH2 — ethyl group
IUPAC RULES International Union of Pure and Applied Chemistry Consider all alkyl groups attached to it as branch chains or substituents that have replaced hydrogen atoms of the parent hydrocarbon. If two chains of equal length are found, use the chain that has the larger number of substituents attached to it. The alkane’s name consists of the parent compound’s name prefixed by the names of the alkyl groups attached to it. RULE 1. Select the longest continuous chain of carbon atoms as the parent compound.
This chain has 6 carbon atoms. 1 2 3 4 6 5 This chain has 4 carbon atoms. 1 2 3 4 This structure has 2 chains.
This is the longest continuous chain. 1 2 3 4 5 6 Select this chain as the parent compound.
1 2 3 4 5 6 This is a methyl group. It is a branch chain and can be considered to have replaced a hydrogen on the parent compound.
3 The name of the compound is 3-methylhexane. 3 1 2 3 4 5 6
IUPAC RULES If the first subsitutent from each end is on the same-numbered carbon, go to the next substituent to determine which end of the the chain to start numbering. RULE 2. Number the carbon atoms in the parent carbon chain starting from the end closest to the first carbon atom that has an alkyl group substituted for a hydrogen atom.
1 2 3 4 5 6 7 8 If the chain is numbered left to right, the isopropyl group is on carbon 5. isopropyl group
8 7 6 5 4 3 2 1 If the chain is numbered right to left, the isopropyl group is on carbon 4. Use right to left numbering so that the isopropyl group is on the lowest numbered carbon. 4-isopropyloctane isopropyl group
IUPAC RULES RULE 3. Name each alkyl group and designate its position on the parent carbon chain by a number (e.g., 2-methyl means group attached to C-2). 5 4 3 2 1 2-isopropyl pentane
RULE 4. When the same alkyl-group branch chain appears more than once, indicate this repetition by a prefix (di-, tri-, tetra- and so forth) written in front of the alkyl group name (e.g. dimethyl indicates two methyl groups). • –The numbers indicating the alkyl-group positions are separated by a command and followed by a hyphen and are placed in front of thename (e.g., 2,3-dimethyl). 5 4 3 2 1 The methyl group appears twice 2,3-dimethylpentane
RULE 5. When several different alkyl groups are attached to the parent compound, list them in alphabetical order (e.g. ethyl before methyl in 3-ethyl-4-methyloctane). Prefixes are not included in alphabetical ordering (ethyl comes before dimethyl).
methyl ethyl 3-ethyl-4-methyloctane 1 2 3 3 4 4 5 6 7 8
Alkanes can have many different types of substituents. • For example:
CYCLIC HYDROCARBONS • A hydrocarbon that contains carbon atoms joined to form a ring. • Cycloalkanes – all carbons of the ring are saturated
NOMENCLATURE OF CYCLOALKANES • Similar to that alkanes. For examples:
ISOMERISATION • Structural isomers: • Molecules that have the same molecular formula, but different structure Three isomers of pentane (C5H12)
ALKENES • Also called olefins • Contain at least one carbon-carbon double bond (C=C) • General formula, CnH2n (n=2,3,…) • Classified as unsaturated hydrocarbons (compound with double or triple carbon-carbon bonds that enable them to add hydrogen atoms. • sp2-hybridized • For example: C2H4 - ethylene
ALKYNES • Alkynes contain at least carbon-carbon triple bond. • General formula: CnH2n-2, where n = 2, 3,…. • Alkyne nomenclature: • Used suffix –yne • Same as alkene nomenclature
IUPAC RULES RULE 1. Select the longest continuous carbon chain that contains a double or triple bond. This chain contains 6 carbon atoms
RULE 2. Name this compound as you would an alkane, but change –ane to –ene for an alkene and to –yne for an alkyne. Name the parent compound octene. This chain contains 8 carbon atoms This is the longest continuous chain. Select it as the parent compound.
RULE 2. Name this compound as you would an alkane, but change –ane to –ene for an alkene and to –yne for an alkyne. This chain contains a triple bond. Name the parent compound octyne.
RULE 3. Number the carbon chain of the parent compound starting with the end nearer to the double or triple bond. Use the smaller of the two numbers on the double- or triple-bonded carbon to indicate the position of the double or triple bond. Place this number in front of the alkene or alkyne name.
IUPAC RULES This end of the chain is closest to the double bond. Begin numbering here.
IUPAC RULES The name of the parent compound is 1-octene. 4 3 2 1 5 6 7 8
IUPAC RULES 4 3 2 1 5 6 7 8 The name of the parent compound is 1-octyne.
RULE 4. Branched chains and other groups are treated as in naming alkanes. Name the substituent group, and designate its position on the parent chain with a number.
IUPAC RULES The ethyl group is attached to carbon 4. This is an ethyl group. 4 4 3 2 1 5 6 4-ethyl-1-octene 7 8
IUPAC RULES The ethyl group is attached to carbon 4. 4 4 3 2 1 5 6 4-ethyl-1-octyne 7 8
must specify whether the molecule is cis or trans (geometric isomer) • cis – two particular atoms (or groups of atoms) are adjacent to each other • trans – the two atoms (or groups of atoms) are across from each other
CYCLOALKENES • Contains C=C in the ring • Nomenclature of cycloalkenes: • Similar to that alkenes • Carbons atoms in the double bond are designated C1 and C2
AROMATIC HYDROCARBONS • Contain one or more benzene rings Benzene Kekulé Structure 6 carbons in a ring 3 double bonds
The structure of benzene can be represented in two abbreviated ways. The corner of each hexagon represents a carbon and a hydrogen atom.
A substituted benzene is derived by replacing one or more of benzene’s hydrogen atoms with an atom or group of atoms. A monosubstituted benzene has the formula C6H5G where G is the group that replaces a hydrogen atom. All hydrogens in benzene are equivalent. It does not matter which hydrogen is replaced by G.