Organic Chemistry

Why “Organic?” From the word “Organism” Until 19thC, belief that these compounds came from tissues of living organisms. Bef.1828: organic compounds obtained from remains of organisms VITALISM: A “vital force” from living organisms was needed to make an organic compound.

The birth of a new organic chemistry 1828, German Friedrich Wöhler synthesized UREA (as found in urine) from inorganic ammonium cyanate (NH4)OCN. Organic chemistry: the chemistry of carbon-containing compounds Of tens of millions of known compounds, >95% are compounds of carbon

Common Elements in Organic Compounds C, H, O, (N, S)

The Secret to Organic Compounds: the unique carbon atom CATENATION Ability of C-atoms to bond to each other so strongly, they can form long chains. Eg. Thousands of C-atoms bonded. Each carbon can have four bonds, maximum

Common organic compound families HYDROCARBONS: Only C and H Alkanes, alkenes, alkynes, arenes, aromatic compounds OXYGEN-CONTAINING Alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, acid anhydrides NITROGEN-CONTAINING Amines, Amides

Classification of Hydrocarbons 24.1

Alkanes Alkanes have the general formula CnH2n+2 where n = 1,2,3,… only single covalent bonds saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule CH4 C2H6 C3H8 methane ethane propane 24.2

Structural isomers are molecules that have the same molecular formula but different structures 24.2

How many structural isomers does pentane, C5H12, have? n-pentane C H CH3 2,2-dimethylpropane 2-methylbutane 24.2

Alkane Nomenclature The parent name of the hydrocarbon is that given to the longest continuous chain of carbon atoms in the molecule. CH3 CH2 CH 4-methylheptane 1 2 3 4 5 6 7 An alkane less one hydrogen atom is an alkyl group. CH4 methane CH3 methyl 24.2

Alkane Nomenclature 24.2

Alkane Nomenclature When one or more hydrogen atoms are replaced by other groups, the name of the compound must indicate the locations of carbon atoms where replacements are made. Number in the direction that gives the smaller numbers for the locations of the branches. CH3 CH CH2 1 2 3 4 5 2-methylpentane CH3 CH2 CH 1 2 3 4 5 4-methylpentane 24.2

Alkane Nomenclature Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind. CH3 CH CH2 1 2 3 4 5 6 2,3-dimethylhexane CH3 CH C CH2 1 2 3 4 5 6 3,3-dimethylhexane 24.2

Alkane Nomenclature Use previous rules for other types of substituents. CH3 CH Br 1 2 3 4 NO2 2-bromo-3-nitrobutane CH2 CH CH3 Br 1 2 3 4 NO2 1-bromo-3-nitrobutane 24.2

What is the IUPAC name of the following compound? CH3 CH CH2 C2H5 1 2 3 4 5 6 7 8 2-methyl-4-ethyloctane What is the structure of 2-propyl-4-methylhexane? 1 2 3 4 5 6 CH3 CH CH2 C2H5 24.2

Cycloalkanes Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,… 24.2

Alkenes Alkenes have the general formula CnH2n where n = 2,3,… contain at least one carbon-carbon double bond also called olefins CH2 CH CH3 CH3 CH 1-butene 2-butene C Cl H C Cl H cis-dichloroethylene trans-dichloroethylene 24.2

Alkynes Alkynes have the general formula CnH2n-2 where n = 2,3,4,… contain at least one carbon-carbon triple bond CH C CH2 CH3 CH3 C 1-butyne 2-butyne Production of acetylene CaC2 (s) + 2H2O (l) C2H2 (g) + Ca(OH)2 (aq) 24.2

August Kekule and the Dream C6H6

"I fell into a reverie, and lo, the atoms were gamboling before my eyes! Whenever, hitherto, these diminutive beings had appeared to me, they had always been in motion; but up to that time, I had never been able to discern the nature of their motion. Now, however, I saw how, frequently, two smaller atoms united to form a pair; how a larger one embraced the two smaller ones; how still larger ones kept hold of three or even four of the smaller; whilst the whole kept whirling in a giddy dance. I saw how the larger ones formed a chain, dragging the smaller ones after them, but only at the ends of the chain. . . The cry of the conductor: “Clapham Road,” awakened me from my dreaming; but I spent part of the night in putting on paper at least sketches of these dream forms. This was the origin of the Structural Theory." "...I was sitting writing on my textbook, but the work did not progress; my thoughts were elsewhere. I turned my chair to the fire and dozed. Again the atoms were gamboling before my eyes. This time the smaller groups kept modestly in the background. My mental eye, rendered more acute by the repeated visions of the kind, could now distinguish larger structures of manifold conformation; long rows sometimes more closely fitted together all twining and twisting in snake-like motion. But look! What was that? One of the snakes had seized hold of its own tail, and the form whirled mockingly before my eyes. As if by a flash of lightning I awoke; and this time also I spent the rest of the night in working out the consequences of the hypothesis."

Aromatic Hydrocarbons 24.3

Aromatic Compound Nomenclature CH2CH3 ethylbenzene NH2 aminobenzene Cl chlorobenzene NO2 nitrobenzene Br Br 1 2 3 4 5 6 1,2-dibromobenzene 1,3-dibromobenzene 24.3

Polycyclic Aromatic Hydrocarbons 24.3