550 likes | 701 Vues
Organic Chemistry. The chemistry of compounds containing carbon.
E N D
Organic Chemistry • The chemistry of compounds containing carbon.
Refinery and tank storage facilities, like this one in Texas, are needed to change the hydrocarbons of crude oil to many different petroleum products. The classes and properties of hydrocarbons form one topic of study in organic chemistry.
hydrocarbons • A hydrocarbon is a compound consisting of only hydrogen and carbon. • The carbon to carbon can be single, double, or triple bonds. • The bonds are always nonpolar.
HYDROCARBONS an organic compound (as acetylene or butane) containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal, and bitumens Here are some Characteristics of hydrocarbons: Has non-polar molecules sp3 hybridization Contains only hydrogen and carbon non-electrolytes because of poor ionization In "most** situations, it is not soluble in water The reactivity is very slow The low boiling point makes it pretty easy to decompose Presented by Brent Daigle, Ph.D. (ABD)
Carbon-to-carbon bonds can be single (A), double (B), or triple (C). Note that in each example, each carbon atom has four dashes, which represent four bonding pairs of electrons, satisfying the octet rule.
Carbon-to-carbon chains can be (A) straight, (B) branched, or (C) in a closed ring. (Some carbon bonds are drawn longer, but are actually the same length.)
Classification of Organic MoleculesFunctional Groups • Hydrocarbons - molecules that possess only hydrogen and carbon • a1. Alkanes – noncyclic hydrocarbons with only C-C single bonds. • Formula CnH2n+2 where n is an integer. Example: Butane CH3CH2CH2CH3 C4H10 a2. Cycloalkanes – cyclic hydrocarbons with only C-C single bonds. Formula CnH2n where n is an integer. Example:CyclobutaneC4H8 b1. Alkenes – noncyclic hydrocarbons with C=C double bonds. Formula CnH2n where n is an integer. Example: 2-Butene CH3CH=CHCH3 C4H8
b2. Cycloalkenes – cyclic hydrocarbons with C=C double bonds. Formula CnH2n-2 where n is an integer. Example:Cyclobutene C4H6 c. Alkynes – noncyclic hydrocarbons with C≡C triple bonds. Formula CnH2n-2 where n is an integer. Example:Butyne CH3C≡ CCH3C4H6 d. Aromatic Hydrocarbons – benzene and its derivatives or C6H6
2. Compounds containing Oxygen a. Alcohols R-OH Functional Group OH hydroxyl group CH3OH methyl alcohol HOCH2CH2OH ethylene glycol (antifreeze) b. Ethers R-O-R CH3CH2-O-CH2CH3Diethylether c. Aldehydes and Ketones Functional Group C=O carbonyl group
Carboxylic Acids • Functional Group -CO2H -COOH -COH Carboxyl Group O Acetic Acid e. Derivatives of Carboxylic Acids Ester Acid Chloride Amide
3. Nitrogen-Containing Molecules a. Amines R-NH2 Functional Group -NH2 amino group Amines are Lewis and Bronsted bases because of the nonbonded pair of electrons .. b. Amides (see above) c. Nitriles Functional Group Cyano Group
Single versus Double Bonds Ethane The carbon-carbon single bond in ethane freely rotates at room temperature. Pi bond broken Ethylene The carbon-carbon double bond in ethylene does not freely rotate at room temperature. Why not? Answer: The Pi bond would have to be broken. It will not break at room temperature
Isomers – different compounds with the same formula • Constitutional (Structural) Isomers – isomers that differ in their bonding sequence C5H12 C5H12 C2H2BrCl C2H2BrCl b. Stereoisomers – isomers that differ in their spatial orientation C2H2BrCl C2H2BrCl Cis isomer Trans isomer
Use of Wedges and Dashed Lines Solid Wedge indicates “coming toward you” Dashed Line indicates “going away” Narrow Line indicates “in the plane of paper” Question: Are the above cycloalkanes constitutional or stereoisomers? Answer: Stereoisomers
ALKANE • Alkanes are hydrocarbons with only single bonds. • SATURATED HYDROCARBONS – they contain only C & H • they have only C-C and C-H single bonds • Contain the maximum possible number of H per C • Occasionally referred to as ALIPHATIC compounds;Greek aleiphas, meaning fat (many animal fat contain long carbon chains similar to alkanes) • Alkanes occur in what is called a homologous series. • Each successive compound differs from the one before it only by a CH2
The Alkanes Characteristics AKA Paraffins, are chemical compounds that consist only of the elements carbon (C) and hydrogen (H). Each are linked by a single bond. Each carbon atom must have 4 bonds (either C-H or C-C bonds), and each hydrogen atom must be joined to a carbon atom (H-C bonds). General formula CnH2n+2 (Linear saturated hydrocarbon) Brent Daigle, Ph.D. (ABD)
Chemical structure of methane Methane the simplest alkane Tetrahedral 109.5o MW=16 g/ml • PHYSICAL PROPERTIES • Non-polar – comparable EN of C & H; symmetrical cmpd. • Low b.p. (-161.5o), or low m.p.(-83o) – weak VW attraction. • Colorless • Sp. Gravity = 0.4 g/mL • Slightly soluble in water • SOURCES: • END PRODUCT OF ANAEROBIC DECAY OF PLANT AND ANIMALS • It is a major constituent of natural gas (97%) • Fire damp of coal mines • Marsh gas bubbling in swamp • Methane can be isolated by fractional distillation • OXIDATION BY HALOGENS (HALOGENATION)
The Alkanes Methane H H C H CH4 H Ethane H H H C C H C2H6 H H Propane H HH H C CC H C3H8 H HH Presented by Brent Daigle, Ph.D. (ABD)
Vocabulary Review (Time to pull out the ‘ole Latin Textbook) The number of carbon atoms = root name! • meth 1 carbon • eth 2 carbon • prop 3 carbon • but 4 carbon • pent 5 carbon • hex 6 carbon • hept 7 carbon • oct 8 carbon • non 9 carbon • dec 10 carbon Presented by Brent Daigle, Ph.D. (ABD)
Physical Properties of Alkanes 1. Combustion - Alkanes are flammable, i.e. they burn. 2 2 2. Boiling and melting points a. Both bp and mp increase with increasing carbon number for straight-chain alkanes with formula CnH2n+2 Carbon Number Physical State C1- C4 gases C5 – C16 liquids C17 – C30 oils and greases C30 – C50 paraffin waxes >C50 plastics (polyethylene)
b. Branching tends to lower the boiling point and raise the melting point BP 60oC 58oC 50oC MP -154oC -135oC -98oC Explanation: MPBranching reduces the flexibility of the molecule which reduces the entropy term S in the equation Tmp= H/S. Since S is in the denominator, Tmpincreases. BP Branching reduces surface area (more compact structure), and therefore London dispersion forces which control boiling point for these molecules. 3. Solubility – alkanes are nonpolar molecules and therefore insoluble in water, which is polar. Alkanes are hydrophobic. 4. Densities – alkanes are less dense than water, with densities near 0.7 g/mL. Therefore they float on water, e.g. Exxon Valdez oil spill.
Petroleumis a mixture of alkanes, cycloalkanes, and aromatic hydrocarbons. • Petroleum is formed from the slow decomposition of buried marine life, primarily plankton and algae. • As petroleum is formed it is forced through porous rock until it reaches an impervious layer of rock. • Here it forms an accumulation of petroleum and saturated the porous rock creating an oil field.
Crude oilis the petroleum that is pumped directly from the ground. • It is a complex mixture of hydrocarbons with one or two carbon atoms up to a limit of about 50 carbon atoms. • This is usually not useful, so it must separated by distillation.
Crude oil from the ground is separated into usable groups of hydrocarbons at this Louisiana refinery. Each petroleum product has a boiling point range, or "cut," of distilled vapors that collect in condensing towers.
The octane rating scale is a description of how rapidly gasoline burns. It is based on (A) n-heptane, with an assigned octane number of 0, and (B) 2,2,4-trimethylpentane, with an assigned number of 100.
Octane Number Straight-chain hydrocarbons have low octane and make poor fuels. Octane Number = 0 heptane Branched Alkanes burn more slowly and reduce the knocking in the engine. Octane Number = 100 2,2,4-trimethylpentane
1. The first step in petroleum refining is fractional distillation.
Distilling Crude Oil Separate fractions based on differences in boiling point.
2. Upstream processing of the distillates. a. Catalytic hydrocracking – produces small alkanes from large alkanes by adding hydrogen. b. Catalytic cracking – produces small alkenes and alkanes by cracking in the absence of hydrogen. c. Catalytic Reforming – the alkanes and cycloalkanes are upgraded to higher octane number by conversion into aromatic compounds.
Alkyl Groups • Removing HYDROGEN from an alkane, the partial structure that remains is called an ALKYL GROUP. • Are NOT stable compounds themselves, they are simply PARTS of larger compounds. • Are named by replacing the –aneending of the parent alkane with a –ylending.
In naming alkyl groups: the prefixes sec- (for secondary) and tert- (for tertiary) used for the C4 alkyl groups, refers to the number of other carbon atoms attached to the branching carbon atom. • There are 4 possibilities: primary (1o), secondary (2o), tertiary (3o) and quaternary (4o).