ORGANIC CHEMISTRY Hydrocarbons: Alkanes, Alkenes, and Alkynes
Organic chemistry The study of carbon compounds The first known organic compounds were derived from animal and vegetable sources and were difficult to crystallize and purify. Swedish chemist Torbern Bergman was the first person to express the difference between “organic” and “inorganic” substances, and the phrase organic chemistry soon to came to mean “the chemistry of compounds from living organisms”.
Organic Chemistry To many chemist at that time, their only explanation for the difference in behavior between organic and inorganic compounds was that organic compounds contained a peculiar and “vital force” (vital force theory) as a result of their derivation from living sources. Michel Chevreul (1816) Animal fat NaOH soap + Glycerine Soap H3O+ “fatty acids”
Organic Chemistry Friedrich Wohler (1828) - it was possible to convert the “inorganic” salt, ammonium cyanate, into “organic” substance, urea. O NH4+-OCN heat H2 N C NH2
Why is Carbon special? Why is it that sets Carbon apart from all other elements in the periodic table? -The unique ability of carbon to bond together forming long chains and rings. Carbon, alone of all elements, is able to form an immense diversity of compounds, from the simplest to the staggeringly complex: from methane to DNA, which can contain hundreds of billions.
Important Families of Organic CompoundsHydrocarbons Only C and H presentAlkanes Single bondAlkenes Double bondAlkynes Triple bondAromaticAlcohols R O HEthers R O R’ OAldehydes R C H OKetones R C R OEsters R C OR
OCarboxylic acids R C OH R’’(H)Amines R N R’(H) O RAmides R C N R
HYDROCARBONS Hydrocarbons are organic compounds that consist of only C and H atoms. Hydrocarbons come in a variety of forms. They may be gases (methane and paropane), liquids (hexane and benzene), waxes (paraffin wax), or polymers (polyethylene and polystyrene). Hydrocarbons can be processed to create plastics. They are insoluble in water.
HYDROCARBONS The simplest class of organic compounds. Nonpolar There are four main types of hydrocarbons: - saturated hydrocarbons (alkanes) - unsaturated hydrocarbons (alkenes or alkynes) - cycloalkanes - aromatic hydrocarbons
HYDROCARBONS SATURATED means that each carbon is bonded to four other atoms through single covalent bonds. Hydrogen atoms usually occupy all available bonding positions after the carbons have bonded to each other. UNSATURATED hydrocarbons contain either double or triple bonds. Since the compound is unsaturated with respect to hydrogen atoms, the extra electrons are shared between 2 carbon atoms forming double or triple bonds.
ALKANES made up of only carbon and hydrogen atoms Also called “paraffins” single bonds only between carbon atoms general formula: CnH2n+2 (assuming non-cyclic structures) name ends in "ane"
Alkanes Many of these (alkanes) substances are familiar because of their widespread use. Example: Methane (CH4 ), a major component of natural gas - propane (C3H8), major component of bottled gas - butane (C4H10), used in disposable lighters and in fuel canisters for gas camping stoves and lanterns. - alkanes with from 5 to 12 carbon atoms per molecule are found in gasoline.
IUPAC NOMENCLATUREKey Concepts: - Name and number the longest carbon chain as for a straight chain alkane Identify each of the branches (side-chains). Use the lowest number combinations for the branches (side-chains). Name each branch or side-chain (alkyl group) : methyl CH3 ethyl C2H5 propyl C3H7
Nomenclature For more than 1 of the same alkyl group use: di = 2 tri = 3 tetra = 4 Use commas between numbers, eg, 1,2 or 2,3 Use hyphens between numbers and words, eg, 2-methyl or 2,3-dimethyl If there is more than 1 type of branch or side-chain, arrange their names alphabetically, ie, ethyl groups are named before methyl groups which are named before propyl groups
Structural Isomers Isomers - compounds with the same molecular formula butdifferent in structures.EXAMPLE: C4H10 H H H H H H H H - C – C – C - C- H H-C–C–C–H H H H H H H(CH3CH2CH2CH3 ) CH3
Sample exercises Name the following alkane:1. CH3 CH3 CH3CH – CHCH2CH2CH32. CH3 CH3 - CH2 – CH2 – CH2 – CH – CH2 – CH3
Sample Exercises: Write the structural formula for?1. 3-ethyl,3-methylheptane2. 2-methylbutane3. 2,2-dimethylpropane
Reaction of Alkane Combustion Alkane reacts with O2 to produce CO2 and Water CH4 + 2 O2 → 2 H2O + CO2 + Energy C3H8 + 5 O2 → 4 H2O + 3 CO2 + Energy
ALKENES containing a carbon- carbon double bond Also called as “Olefins” More reactive than alkanes General formula: CnH2n(where n is any integer)
Naming Alkenes and Alkynes Name the longest carbon chain that contains the double or triple bond (see table). The name for the alkenes ends in ene instead of – ane. The name for the alkynes ends in –yne instead of – ane. Number the main chain from the end nearest the double or triple bond. Indicate the position of the double or triple bond with the number of the first unsaturated carbon. Place the number and names of substituents in front of the alkene or alkyne name.
AlkenesThe simplest alkenes are ethylene and propylene.They are the two most important organic chemicals produced industrially.Ethylene is a plant hormone. It plays important roles in seed germination and ripening of fruits.For alkenes with four or more carbon atoms, several isomers (same formula but different structures) exist for each molecular formula.
AlkenesFor example: C4H8 H3C CH3 H3C H C=C C=C H H H 3C H cis-2-butene 2-methylpropene CH3 H2C H H3C H C=C C=C H H H CH3 1-butene trans-2-butene
Geometric Isomers (cis and trans) - compounds that have the same molecular formula and the same groups bonded to one another but differ in the spatial arrangement of these groups.
Sample Exercises:Give the name of the ff. alkenes:1. CH3 CH3 - CH2 – CH2– CH – CH = CH - CH32. Br CH3 CH2 CH=CCH3
Sample Exercises Give the structural formula for:1. 1,4-pentadiene2. 3-ethyl-1-hexene3. tra ns -2,3-dichloro-2-butene4. 1,3,5-hexatriene
ALKYNES C C bonds More reactive than alkanes and alkenes General formula: CnH2n-2 Highly reactive molecules
Alkynes C2H2, ethyne or acetylene is the most simplest alkyne and it is highly reactive molecule. When acetylene is burned in a stream of oxygen in an oxyacetylene torch, the flame reaches a very high temperature, about 3200 K.
Nomenclature of Alkynes Sa m e with A ne s … . . lke However, when there is a choice in numbering, d o uble bo nd s re c e ive lo we r num be rs tha n trip le bo nd s …..Example: CH3CH CHC CCH2CH3 2-heptene-4-yne