Functional Groups Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 1 Elements in Organic Compounds In organic molecules, carbon atoms bond • with four bonds. • mostly with H and other C atoms. • sometimes to O, N, S, • sometimes to halogens F, Cl, and Br. 2 Functional Groups Functional groups are • a characteristic feature of organic molecules that behave in a predictable, similar way. • composed of an atom or group of atoms. • groups that replace a hydrogen atom in the corresponding alkane. • a way to classify families of organic compounds. 3 Alkenes and Alkynes Alkenes contain a double bond between adjacent carbon atoms. (Double bond: 4 electrons) Alkynes contain a triple bond. (Triple bond: 6 electrons) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Organic compounds with Carbon-Oxygen bonds 1. Alcohols An alcohol contains the hydroxyl (-OH) functional group. (instead of an H in that place) Ethanol Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings OH- vs -OH • OH- : hydroxide anion found in bases (e.g NaOH) • -OH: hydroxyl group colvalently bound to carbon atom in an organic compound (e.g. ethanol CH3-CH2OH) 6 2. Ethers In an ether, an oxygen atom is bonded to two carbon atoms. –C–O–C– . has a common name that gives the alkyl names of the attached groups followed by ether. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Diethyl ether 7 3. Aldehydes An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom. formaldehyde Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings acetaldehyde 8 4. Ketones In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms. Acetone Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 9 5. Carboxylic Acids and Esters Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. O ║ — C—OH Acetic acid Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 10 5. Esters An ester contains the carboxyl group between carbon atoms. Methyl acetate Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 11 Organic compounds with CarbonNitrogen bonds 1. Amines In amines, the functional group is a nitrogen atom. H H C —N – H or C —N —C Methyl amine Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Dimethyl amine 12 2. Amides In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group (-NH2). acetamide Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 13 Functional Groups Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 14 Learning Check Classify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine or amide. 1) CH3─CH2─CH2─OH 2) CH3─O─CH2─CH3 3) CH3─CH2─NH2 O ║ 4) CH3─C─OH carboxylic acid alcohol ether amine O ║ 5) CH3─C─O─CH3 ester 15 Unsaturated Hydrocarbons Cis-Trans Isomers Chapter 11.2 16 Cis and Trans Isomers In an alkene the double bond, • is rigid. • holds attached groups in fixed positions. • makes cis/trans isomers possible. CH3 CH = CH cis CH3 CH3 CH = CH trans CH3 17 Cis-Trans Isomers In cis-trans isomers • there is no rotation around the double bond in alkenes. • groups attached to the double bond are fixed relative to each other. You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other. 18 Cis-Trans Isomers Two isomers are possible when groups are attached to the double bond are different. (a double bond cannot rotate) • In a cis isomer, groups are attached on the same side of the double bond. • In the trans isomer, the groups are attached on opposite sides. 19 Cis-Trans Isomerism • Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups. Identical HH C HH Identical Brr BH Br H C C CH3 2-bromopropene (not cis or trans) H C Br 1,1 dibromoethene (not cis or trans) 20 Cis-Trans Isomers in Nature • Insects emit tiny quantities of pheromones, which are chemicals that send messages. • The silkworm moth attracts other moths by emitting bombykol, which has one cis and one trans double bond. 21 Organic Compounds with Oxygen and Sulfur 12.1 Alcohols, Ethers, and Thiols Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 22 Alcohols An alcohol contains a hydroxyl group (—OH) attached to a carbon chain. A phenol contains a hydroxyl group (—OH) attached to a benzene ring. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings water alcohol phenol 23 Naming Alcohols The names of alcohols • in IUPAC replace the -e with -ol. • with common names use the name of the alkyl group followed by alcohol. Formula IUPAC CH4 methane CH3─OH methanol CH3─CH3 ethane CH3─CH2─OH ethanol Common Name methyl alcohol ethyl alcohol 24 Classification of Alcohols Classification of alcohols is • determined by the number of alkyl groups attached to the carbon bonded to the hydroxyl. • primary (1°), secondary (2°), or tertiary(3). Primary (1º) 1 group H | CH3—C—OH | H Secondary (2º) Tertiary (3º) 2 groups 3 groups CH3 CH3 | | CH3—C—OH CH3—C—OH | | H CH3 25 Thiols Thiols • are carbon compounds that contain a –SH group. • are named in the IUPAC system by adding thiol to the alkane name of the longest carbon chain. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 26 Thiols Thiols • often have strong odors. • are used to detect gas leaks. • are found in onions, oysters, and garlic. 27 Properties of Alcohols, Ethers, and Thiols Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 28 Boiling Points of Alcohols Alcohols • contain polar OH groups. • form hydrogen bonds with other alcohol molecules. • have higher boiling points than alkanes and ethers of similar mass. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 29 Boiling Points of Ethers Ethers • do not have a polar group. • have an O atom, but there is no H attached. • cannot form hydrogen bonds between ether molecules. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 30 Solubility of Alcohols and Ethers in Water Alcohols and ethers • are more soluble in water than alkanes because the oxygen atom can hydrogen bond with water. • with 1-4 C atoms are soluble, but not with 5 or more C atoms. 31 Comparing Solubility and Boiling Points Molar Compound Mass Alkane CH3─CH2─CH3 44 Ether CH3─O─CH3 Alcohol CH3─CH2─OH Boiling Soluble Point (°C) in Water? -42 No 46 -23 Yes 46 78 Yes 32 Solubility of Phenol Phenol • is soluble in water. • has a hydroxyl group that ionizes slightly (weak acid). • is corrosive and irritating to skin. OH O + H2O - + H3O+ 33 Combustion of Alcohols Alcohols undergo combustion with O2 to produce CO2 and H2O. 2CH3OH + 3O2 2CO2 + 4H2O + Heat Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 34 Oxidation and Reduction In an oxidation, • there is an increase in the number of C-O bonds. • there is a loss of H. In a reduction, • there is an decrease in the number of C-O bonds. • there is a gain of H. 35 Oxidation and Reduction 36 Oxidation of Primary (1) Alcohols When a primary alcohol is oxidized, [O], • one H is removed from the –OH. • another H is removed from the carbon bonded to the OH. • an aldehyde is produced. [O] Primary alcohol Aldehyde OH O | [O] || CH3—C—H CH3—C—H + H2O | H Ethanol Ethanal (ethyl alcohol) (acetaldehyde) 37 Oxidation of Secondary (2) Alcohols When a secondary alcohol is oxidized, [O], • one H is removed from the –OH. • another H is removed from the carbon bonded to the OH. • a ketone is produced. [O] secondary alcohol ketone OH O │ [O] ║ CH3─C─CH3 CH3─C─CH3 + H2O │ H isopropyl alcohol dimethyl ketone 38 Oxidation of Tertiary Alcohols Tertiary 3alcohols do not readily oxidize. [O] Tertiary alcohol no reaction OH │ [O] CH3─C─CH3 no product │ CH3 no H on the C-OH to oxidize 2-methyl-2-propanol 39
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