Chapter 22

“Functional Groups”

Functional Groups

Most organic chemistry involves substituents

often contain O, N, S, or Palso called “functional groups”- they are the chemically functional part of the molecule, and are the non-hydrocarbon part

Functional Groups

Functional group - a specific arrangement of atoms in an organic compound, that is capable of characteristic chemical reactions.

What is the best way to classify organic compounds? By their functional groups.

Functional Groups

The symbol “R” is used to represent any carbon chains or ringsImportant: Table 22.2, page 589 shows some of the major functional groups - KNOW THESE.

Halogen Substituents

Halocarbons - class of organic compounds containing covalently bonded fluorine, chlorine, bromine, or iodine

General formula: R-X (X = halogen)

Naming? Name parent as normal, add the halogen as a substituent (or prefix)

Halogen Substituents

The more highly halogenated the compound is, the higher the b.p.

Few halocarbons found in nature

but, readily prepared and used

halothane and also the hydrofluorocarbons

Substitution ReactionsOrganic reactions often much slowerslower than inorganic reactions

must break strong covalent bondtrying to find new catalysts to use

Substitution - an atom (or group of atoms) replaces another atom or group of atoms

Substitution Reactions

A halogen (shown as “X”) can replace a hydrogen to make a halocarbon:

R-H + X2 R-X + HX

Sunlight is often a sufficient catalyst:

CH4 + Cl2 → CH3Cl + HClUV light

Substitution ReactionsTreating benzene with a halogen? Examples on Page 601

C6H6(l) + Cl2(g) → C6H5Cl(l) + HCl (g)

Halogens on carbon chains are readily displaced by hydroxide ions (OH1-) to make an alcohol + a salt:

R-X + OH1- R-OH + X1-

CH3-Cl + NaOH CH3-OH + NaClMethanol + sodium chloride

Substitution Reactions

CH3-I + KOH CH3-OH + KI

CH3CH2Br + NaOH CH3CH2OH + NaBr

Iodomethane Methanol

Bromoethane Ethanol

Alcohols

Alcohols - a class of organic compounds with an -OH group

The -OH functional group in alcohols is called a “hydroxyl” group; thus R-OH is the formula

How is this different from the hydroxide ion? (covalent bonding with the carbon- not ionic with a metal like bases)

AlcoholsAliphatic alcohols classified into categories according to the number of R groups attached to the carbon with the hydroxyl

1 R group: primary alcohol2 R groups: secondary alcohol3 R groups: tertiary alcohol

AlcoholsBoth IUPAC and common names

For IUPAC:

drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH

parent is the longest chain that contains the carbon with the hydroxyl attached.

Alcohols

The hydroxyl is given the lowest position number

Alcohols containing 2, 3, and 4 of the -OH substituents are named diols, triols, and tetrols respectively

Alcohols

Common names:similar to halocarbons, meaning name the alkyl group, then followed by the word alcoholOne carbon alcohol = methyl alcohol

AlcoholsMore than one -OH substituents are called glycols (ethylene glycol?)

** Examples on page 590**

Phenols - compounds in which a hydroxyl group is attached directly to an aromatic ring. Cresol is the common name of o, m, and p isomers of methylphenol

Properties of Alcohols

Much like water, alcohols are capable of hydrogen bonding between molecules

this means they will boil at a higher temp. than alkanes and halocarbons with a comparable number of atoms

Properties of AlcoholsAlcohols are derivates of water; the -OH comes from water, and thus are somewhat soluble

Alcohols of up to 4 carbons are soluble in water in all proportions; more than 4 carbons are usually less soluble, because the longer carbon chain is more nonpolar

Properties of AlcoholsMany aliphatic alcohols used in laboratories, clinics, and industry

Isopropyl alcohol (2-propanol) is rubbing alcohol; used as antiseptic, and a base for perfume, creams, lotions, and other cosmetics

Ethylene glycol (1,2-ethanediol) - commonly sold as “antifreeze”

Properties of Alcohols

Glycerol (1,2,3-propanetriol) - used as a moistening agent in cosmetics, foods, and drugs; also a component of fats and oilsEthyl alcohol (ethanol) used in the intoxicating beverages; also an important industrial solvent

Properties of Alcohols

Denatured alcohol- means it has been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol).As little as 10 mL of methanol has been known to cause permanent blindness, and 30 ml has resulted in death!

Addition Reactions

The carbon-carbon single bond is not easy to break

In double bonded alkenes, it is easier to break a bond

Addition reaction- substance is added at the double or triple bond location, after it is broken

Addition ReactionsAddition of water to an alkene is a hydration reaction - usually occurs with heat and an acid (such as HCl or H2SO4 acting as a catalyst)

Note sample in the middle of page 590 for the formation of ethanol from ethene + water

Addition Reactions

Addition of hydrogen to produce an alkane is a hydrogenation reaction, which usually involves a catalyst such as Pt or Pd

common application is the manufacture of margarine from unsaturated vegetable oils (making them solid from a liquid)

EthersA class of organic compounds in which oxygen is bonded to 2 carbon groups: R-O-R is formula

Naming? The two R groups are alphabetized, and followed by ether

Two R groups the same? Use the prefix di-

EthersDiethyl ether is the one commonly called just “ether”

was the first reliable general anesthetic

dangerous- highly flammable, also causes nausea

ethers are fairly soluble in water

Aldehydes and KetonesReview:

alcohol has an oxygen bonded to a carbon group and a hydrogen

ether has an oxygen bonded to two carbon groups

An oxygen can also be bonded to a single carbon by a double bond

Aldehydes and Ketones

The C=O group is called the “carbonyl group”

it is the functional group in both aldehydes and ketones

Aldehydes - carbonyl group always joined to at least one hydrogen (meaning it is always on the end!)

Aldehydes and Ketones

Ketones - the carbon of the carbonyl group is joined to two other carbons (meaning it is never on the end)

Aldehydes and KetonesNaming?

Aldehydes: identify longest chain containing the carbonyl group, then the -e ending replaced by -al, such as methanal, ethanal, etc.

Ketones: longest chain w/carbonyl, then new ending of -one; number it?

propanone, 2-pentanone, 3-pentanone

Aldehydes and Ketones

Neither can form intermolecular hydrogen bonds, thus a much lower b.p. than corresponding alcohols

wide variety have been isolated from plants and animals; possible fragrant odor or taste; many common names

Aldehydes and KetonesBenzaldehydeCinnamaldehydeVanillin

See page 592 for structures of these 3

Methanal (the common name is: formaldehyde)

40% in water is formalin, a preservative

Aldehydes and Ketones

Propanone (common: acetone) is a good solvent; miscible with water in all proportions

why is it a good substance used in nail-polish removers? (a powerful solvent-able to dissolve both polar & nonpolar)

The Carboxylic Acids…

Also have a carbonyl group (C=O), but is also attached to a hydroxyl group (-OH) = “carboxyl” group

general formula: R-COOH

weak acids (ionize slightly)

Named by replacing -e with -oic and followed by the word acid

methanoic acid; ethanoic acid

Carboxylic Acids

Abundant and widely distributed in nature, many having a Greek or Latin word describing their origin

acetic acid (ethanoic acid) from acetum, meaning vinegar

many that were isolated from fats are called fatty acids

The Esters…General formula: RCOOR

Derivatives of the carboxylic acids, in which the -OH from the carboxyl group is replaced by an -OR from an alcohol:carboxylic acid + alcohol ester + water

many esters have pleasant, fruity odors- banana, pineapple, perfumes

EstersAlthough polar, they do not form hydrogen bonds (reason: there is no hydrogen bonded to a highly electronegative atom!)

thus, much lower b.p. than the hydrogen-bonded carboxylic acids they came from

Esters

Can be prepared from a carboxylic acid and an alcohol; usually a trace of mineral acid added as catalyst (because acids are dehydrating agents)

Note equation on p. 593

Esters

Naming? It has 2 words:

1st: alkyl attached to single bonded oxygen from alcohol

2nd: take the acid name, remove the -ic acid, add -ate

example on top of page 593

AminesAmines contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, where in one or more hydrogen atoms have been replaced by a substituent such as an alkyl group. Important amines include amino acids, biogenic amines, trimethylamine, and aniline Primary amine Secondary amine Tertiary amine

                                                   

                         

IsomersIsomers are compounds with the same molecular formula but different structural formulas A simple example of isomerism is given by the formula C3H8O (or C3H7OH) and occurs as two isomers: 1 -propanol and 2- propanol

Note that the position of the oxygen atom differs between the two: it is attached to an end carbon in the first isomer, and to the center carbon in the second.There is, however, another isomer of C3H8O which has significantly different properties: methyl-ethyl-ether. Unlike the isomers of propanol, the ether has an oxygen connected to two carbons rather than to one carbon and one hydrogen.

Geometric Isomers

In one, the two chlorine atoms are locked on opposite sides of the double bond. This is known as the trans isomer. (trans : from latin meaning "across" - as in transatlantic).

In the other, the two chlorine atoms are locked on the same side of the double bond. This is know as the cis isomer. (cis : from latin meaning "on this side"

cis & trans isomers differ from each other in their physical properties and to a lesser extent their chemical properties.

Optical Isomers (enantiomers)These two models each have the same groups joined to the central carbon atom, but still manage to be different:

Obviously as they are drawn, the orange and blue groups aren't aligned the same way. Could you get them to align by rotating one of the molecules? The next diagram shows what happens if you rotate molecule B.

They still aren't the same - and there is no way that you can rotate them so that they look exactly the same. These are isomers of each other.They are described as being non-superimposable in the sense that you couldn't slide one molecule exactly over the other one. Something would always be pointing in the wrong direction.These molecules are said to be chiral.Chiral molecules have the same physical properties, but b/c they differ in the 3-D structue they may show different physiological properties. (Aleve,

Oxidation- Reduction ReactionsAll of the previous classes of organic compounds are related by oxidation and reduction reactions

What is oxidation-reduction?

Oxidation: the gain of oxygen, loss of hydrogen, or loss of e-1

Reduction: the loss of oxygen, gain of hydrogen, or gain of e-1

Oxidation- Reduction Reactions

Oxidation and reduction reactions (sometimes called redox) are coupled- one does not occur without the other

The number of Oxygen and Hydrogen attached to Carbon indicates the degree of oxidation

Oxidation- Reduction ReactionsThe fewer the # of H on a C-C bond, the more oxidized the bond

Thus, a triple bond is more oxidized than a double bond and a single bond

An alkane is oxidized (loss of H) to an alkene, and then to an alkyne

Oxidation- Reduction Reactions

Loss of hydrogen is called a dehydrogenation reaction

may require strong heating and a catalyst

Oxidation- Reduction ReactionsMethane can be oxidized in steps to carbon dioxide methane methanol methanal methanoic acid CO2

the more reduced (more H) a carbon compound, the more energy it can release upon oxidation