Organic Chemistry Study of molecular compounds of carbon

Organic Compounds Inorganic Compounds –include all compounds of carbon except the oxides (carbon dioxide, carbonate, carbide, cyanide, carbon monoxide). -3 to 4 million known organic compounds. Inorganic Compounds -all other substances -50,000 known inorganic compounds.

Two groups or organics: Hydrocarbons – compounds containing only hydrogen and carbon. (ex. methane, butane, octane) Hydrocarbon derivatives – contain carbon, hydrogen and at least one other element. (ex. organic halides, alcohols, carboxylic acids, esters,

Unique Nature of Carbon 1. Carbon atoms have a bonding capacity of 4 2. Carbon atoms can bind together to form rings, sheets, tubes and spheres of almost any size 3. Carbon can form single, double or triple bonds with other elements (no other atom can do this)

Organic compounds are classified into families based upon: 1. Types of bonds present (single, double, etc.) 2. Characteristic structures (rings, chains, branches) 3. Presence of functional groups (halogens (F, Cl, Br and I), alcohols (OH), carboxylic acids (COOH), that determine physical and chemical properties 4. Reactivity

Expressing Organic Compounds Sometimes a shortened notation is used to describe certain families of organic compounds: R – indicates a chain of carbon and hydrogen X – indicates a halogen F, Cl, Br, I

Organic diagrams Complete structural diagram – shows all atoms / bonds. Condensed structural diagram – omits CH bonds but shows C-C bonds. CH3 - CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3 Line diagram – shows chains of carbon atoms with lines only where the end of the line represents a carbon and its hydrogen atoms.

Organic Formulas Molecular formulas – communicate which elements are found in a compound. Ex. CH4O Structural formulas – communicate the arrangement of atoms / functional groups in a compound. Ex. CH3OH

Isomers are substances with the same molecular formula but different structures, and therefore, different names. Example: C6H14 has a number of isomers: hexane 2- methylpentane 3- methylpentane 2,2 – dimethylbutane

Homologous Series is a sequence of molecules with similar structures and differing only by the number of repeating units. Examples: methane, ethane, propane, butane

Physical Properties within a Homologous Series Melting point/boiling point – as the number of carbons in the parent chain increases, melting point increases.

Alkanes aliphatic compound. chains of single C-C bonds general formula is CnH2n+2. called saturated because they have the maximum number of hydrogen atoms form straight chains or branched compounds.

Nomenclature (naming): Prefixes are used to describe the number of carbon atoms in a parent chain (longest) or in a branch. 1 = meth 4 = but 7 = hept 2 = eth 5 = pent 8 = oct 3 = prop 6 = hex 9 = non 10 = dec

Nomenclature of Straight Chain Alkanes stem prefix indicates the number of carbons ending –ane indicates that it is a single bonded C-C chain. Ex. propane C3H8 pentane C5H12

Nomenclature of Branched Chain Alkanes longest continuous chain of carbon atoms is named as the parent chain. (It doesn’t matter if the chain is not straight) Number the carbon atoms consecutively starting at the end closest to the branch. Number branch by the number of the carbon atom it is on. Name the branch using the prefix for the number of carbons in the branch and the ending –yl before naming the parent chain.

If there are more than two branches, they are named in alphabetical order (i.e. ethyl, methyl, propyl). If two branches are the same, use the prefixes di, tri, tetra, etc to indicate the number of branches, and the carbon numbers to indicate their locations.

Examples: 2- methylpentane 2,4 - dimethylhexane 3-ethyl-4-methylhexane

Alkenes and Alkynes Alkenes –contain one or more double C=C bonds. (two less H for each double bond or CnH2n ) Alkynes –contain one or more triple bonds. (four less hydrogen for each triple bond or CnH2n-2) Both are said to be unsaturated because they do not contain the maximum number of atoms possible

Nomenclature of Straight Chain Alkenes and Alkynes longest or parent chain of carbon atoms must contain the multiple bond, and the chain is numbered from the end closest to the multiple bond. number that indicates the position of the multiple bond on the parent chain is placed before the ene or yne ending in the parent chain name.

If there is only one possible position for the multiple bond in the parent chain, it is not numbered. If there are two or more multiple bonds, they are numbered with both positions and named with a prefix indicating the number of multiple bonds.

Examples ethyne pent-2-ene octa-1,7-diene

Naming Branched Chain Alkenes and Alkynes double / triple bond numbered with lowest numbers the parent chain. the branches are named and numbered the same as they were with the alkanes. Ex. 2,3 - dimethylpent-2-ene

Physical Properties of Aliphatics Non polar-do not dissolve in water, dissolve in benzene and other non-polar solvents. As # of carbons increase, melting/boiling points increase due to stronger London dispersion forces Ex) small alkanes are gases (methane, propane, butane) medium alkanes are liquids large alkanes are waxy solids

Boiling point of an alkene is lower than the alkane of the same size (alkene has fewer atoms/electrons and weaker LDFs) Ex) ethene b.p = -103.8oC vs ethane b.p = -88.6oC Boiling point of an alkyne is higher than the alkane of the same size (nature of triple bond creates stronger bonds)

Cyclical Hydrocarbons part of the aliphatic group and produce carbon rings. simple cyclo-alkanes have single C-C bonds with no free ends. The general formula is CnH2n. can have double or triple bonds

Naming Cyclical Hydrocarbons same as naming alkanes, alkenes and alkynes except the parent “ring” begins with cyclo. If only one branched chain is present, it is not numbered because it will always be considered to be on the first carbon. For more than one branch, the first branch is on the first carbon and the other branches are numbered so that the second branch has the next lowest number.

Examples cyclobutene 1,2 – dimethylcyclopentane propylcyclopentene

Aromatic Hydrocarbons originally thought to include compounds with an odor or aroma. today are classified as compounds with a benzene ring structure.

Benzene Ring formula C6H6. a cyclical 6 carbon ring with each carbon being bonded to a hydrogen atom. double and single bonds alternate around the ring, and shift position, creates a hybrid exhibiting resonance, which is very stable.

Naming Aromatic Compounds If an alkyl group is attached to a benzene ring, the compound is named with a branch and the parent name is benzene. No number is required if there is only one branch. ethylbenzene

for two or more branched chains, the first alphabetical branch is numbered as carbon 1, and the next branches are given the lowest numbers. Ex. 1,4 – dimethylbenzene In some larger molecules, the benzene ring is a branch and not attached to the end of a chain. In this case, the benzene branch is given the name phenyl. Ex. 2- phenylbutane