Chapter 12 Alkenes, Alkynes, and Aromatic Compounds Compounds with multiple bonds The most important compound with a triple bond is ethyne also known as acetylene; it is used in the oxy acetylene torch. Bombykol, is another natural product that contains double bonds. We will examine the structure of these materials shortly Compounds of carbon and hydrogen with less tha 2n+ 2 hydrogens other than cyclic hydrocarbons Is there any other way of satisfying the octet for carbon in a molecule with a formula C2H4 or C2H2? How many groups around each C? 3 (bonding electrons are not considered to be a group) H H C :: C H H What’s the geometry? triangular How about C2H2? How many groups around each C? 2 HC≡CH What’s the geometry? linear ethene or ethylene What does ethylene have to do with fruit? A systematic way of naming alkenes and identifying identical structures 1. Locate the longest carbon chain in the molecule that contains the double bonds: this identifies the parent alkene 2. Identify the points of branching and count the number of carbons in each branch; name the alkyl branches in the normal way: methyl, ethyl ... 3. Give the double bond the lowest number 4. Identify any stereochemistry parent: 4 carbons: butene CH2 CH3 groups: 2 carbons: ethyl H2C C location: double bond at position 1; ethyl at 2 CH2 CH3 2-ethyl-1-butene no stereochemistry to describe Are these two compounds the same? All these formulas for butane are identical because of rapid rotation about C-C bonds If the two groups are on the same side of the double bond, use cis On opposite sides, use trans no, rotation about C=C bonds does not occur CH2-CH3 CH parent: cyclohexane H2C CH2 groups: ethyl, chloro H2C CH location: 1, 3 CH2 Cl CH2CH3 CH2CH3 Cl Cl The solid wedge is used to denote a group sticking out of the plane of the screen A dotted wedge is used to denote a group sticking out of the plane of the screen Two groups with the same relative orientation is called cis Two groups with the opposite relative orientation is called trans Naming compounds with double and triple bonds ethane generic names alkane H3C CH3 ethene or ethylene alkene H2C CH2 alkyne ethyne or acetylene H CHC H H CC CH3 CH3 cis 2-butene H CH2CH3 H H H H 1-butene H CH2CH3 CH3 H trans 2-butene H CH3 H CC CH2CH3 1-butyne CH3 CC CH3 2-butyne H CH2CH2CH2CH3 Name the following: CC CH3CH2 CH H CH3 parent: nonene groups: methyl, double bond location: 3-methyl, 4-double bond stereochemistry: trans trans 3-methyl-4-nonene H CH3 C H2C CH parent: cyclohexene H2C CH groups: methyl CH2 location: 1, 3 or 1,2? shorthand notation 3-methyl-1-cyclohexene or 1-methyl-2-cyclohexene A pheromone is a chemical messenger emitted by insects in minute quantities. Bombykol is emitted by the silkworm moth to attract other moths and has one cis and one trans double bond 16 C: hexadecane parent alkane 2 double bonds diene alcohol: drop the last e and add ol stereochemistry: cis and trans (CH2)7 means 7 CH2 groups in a row To name this compound we need to know how to name a compound with 16 carbon atoms How to name compounds with more than one double bond How to name alcohols and how to designate “stereochemistry” (the arrangement of groups in space: trans10, cis 12-hexadecadien-1-ol Name the following: Br Br parent: ethene cis-1,2-Dibromoethene groups: bromo A. CC location 1,2 H H stereochemistry cis : CH3 H CC parent: butene trans-2-Butene B. groups: double bond H CH3 location: 2 stereochemistry: trans CH3 Cl parent: propene C. CC groups: chloro location: 1,1-Dichloropropene H Cl 1,1 stereochemistry: none CH3 CH3 CH C 2 CH3 CH C CH CH CH3 2 CH2 CH2 parent: parent: groups: groups: location location stereochemistry: stereochemistry: CH3 C C C C Basic carbon framwork of many natural products CH3 CH3 H C H H C H C C C C C CH C CH2 2 H CH H CH CH CH CH CH CH3 3 3 CH3 2 -methyl-5-isopropyl-1,3-cyclohexadiene Dill Anethum graveolens (Umbelliferae) Dill is a thin, annual originating in the Middle East. Since recorded history it has been cultivated as a medicinal and aromatic herb. It was spread through Europe by way of the monasteries. The picture on the left shows a 'broad-leafed' variety, the original type has completely thready leaflets. The fresh dill leaves and flowers contain an essential oil whose main component is (-)-alpha-phellandrene (ca. 60 %). Draw structures for the following compounds: 1-hexyne 2-methyl-1,7-octadiene 1,2-propadiene Compounds of carbon with multiple bonds to other elements Oxygen double bonded to carbon is called a carbonyl group (C=O) If the carbon of the carbonyl group is attached to two other carbon atoms the compound is called a ketone, An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen. O Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. O acetic acid or ethanoic acid In an ester, the hydrogen on oxygen is replaced by a carbon atom. A nitrogen attached to a carbonyl group is called an amide; the other two groups attached to nitrogen can be either both N carbons, hydrogens or a mix of both carbon and hydrogen A few reactions of unsaturated compounds: Adding H2 to double bonds in vegetable oils produces compounds with higher melting points solids at room temperature, such as margarine, soft margarine, and shortening. This makes them less reactive and less prone to become rancid; rancidness is due to reaction of the double bonds with oxygen O butyric acid CH3CH2CH2 C OH CH3CH2CH2 O H CH3CH2CH2 C O CH2 O CH OCCH CH CH CH 2 2 2 2 2 C O CH OCCH CH CH CH H 2 2 2 2 2 CH2 CH3CH2CH2CH2CHC 2O CH +H2 (catalyst) H CH3CH2CH2CH2CHC 2O CH CH2OCCH2CH2CH2CH2 C H CH2OCCH2CH2CH2CH2 CH2 C O CH2 O CH2CH2CH2CH3 CH2CH2CH2CH3 unsaturated triglyceride saturated triglyceride Polymers are large, long-chain molecules; they are found in nature, including cellulose in plants, starches in food, and proteins and DNA in the body; they are also made synthetically, such as polyethylene and polystyrene, Teflon, and nylon they are made up of small repeating units called monomers that are often alkenes F F Teflon CF2CF2CF2CF2CF2 F F Polypropylene CH3 H CHCH2CHCH2CHCH2CHCH2 H H CH CH CH3 CH3 3 3 Cl H Polyvinyl chloride CHCH2CHCH2CHCH2CHCH H H Cl Cl Cl Cl Recycling is simplified by using codes found on plastic items. Aromatic Compounds H H C H C C C C H C H H Different ways of representing the molecule benzene Molecules that contain a benzene ring are often referred to as aromatic compounds, originally because of their odor CH3 NH2 OH methylbenzene (toluene) aminobenzene (aniline) hydroxybenzene (phenol) OH OH C H H H C H C C C C C C C C H H H C H C CH3 CH2CH2CH3 O O OH O OH OCH3 C C C-OH C C C H CH H OH H OH H CH C C C C C C C C C C C C C C C C C H C H H H H H H C H C H H H H benzoic acid salicylic acid methyl salicylate benzaldehyde 2-hydroxybenzoic acid methyl 2-hydroxybenzoate 1-methyl,2,4,6-trimethylbenzene acetosalicylic acid 4-hydroxy-3- methoxybenzaldehyde H H Cl H H H H H H H H HH Cl naphthalene 1,4-dichlorobenzene benzo[a]pyrene.