Chemistry 2100 Lecture 5

Nomenclature IUPAC names for aldehydes To name an aldehyde, change the suffix -e of the parent alkane to -al. Because the carbonyl group of an aldehyde can only be at the end of a parent chain and numbering must start with it as carbon-1, there is no need to use a number to locate the aldehyde group. For unsaturated aldehydes, indicate the presence of a carbon-carbon double bond by changing the ending of the parent alkane from -ane to -enal. Numbering the carbon chain begins with the aldehyde carbonyl carbon. Show the location of the carbon-carbon double bond by the number of its first carbon.

Nomenclature The IUPAC system retains common names for some aldehydes, including these three.

Nomenclature IUPAC names for ketones. The parent alkane is the longest chain that contains the carbonyl group. Indicate the presence of the carbonyl group by changing the -ane of the parent alkane -one. Number the parent chain from the direction that gives the carbonyl carbon the smaller number. The IUPAC retains the common name acetone for 2-propanone.

Nomenclature To name an aldehyde or ketone that also contains an -OH (hydroxyl) or -NH2 (amino) group: Number the parent chain to give the carbonyl carbon the lower number. Indicate an -OH substituent by hydroxy-, and an -NH2 substituent by amino-. Hydroxyl and amino substituents are numbered and alphabetized along with other substituents.

Nomenclature Common names The common name for an aldehyde is derived from the common name of the corresponding carboxylic acid. Drop the word "acid" and change the suffix -ic or -oic to -aldehyde. Name each alkyl or aryl group bonded to the carbonyl carbon as a separate word, followed by the word "ketone”. Alkyl or aryl groups are generally listed in order of increasing molecular weight.

Physical Properties

Physical Properties

Preparations

(1°) (2°)

(1°) (2°)

(1°) (2°)

(1°) (2°)

(1°) (2°)

Reactions

Z = C, H

  Z = C, H

  Z = C, H

    Z = C, H

    Z = C, H

    Z = C, H

    Z = C, H

    Z = C, H

    Z = X, O, N

    OH Z = X, O, N

 

   

   

   

   

   

   

   

(xs)

(xs)

(xs)

Cyclization

 

   

   

   

   

   

   

   

1 6 6 2 5 5 3 1 4 4 1 4 3 2 3 2 5 6

1 6 6 2 5 5 3 1 4 4 1 4 3 2 3 2 5 6

1 6 6 2 5 5 3 1 4 4 1 4 3 2 3 2 5 6

1 6 6 2 5 5 3 1 4 4 1 4 3 2 3 2 5 6

1 6 6 2 5 5 3 1 4 4 1 4 3 2 3 2 5 6

1 6 2 5 3 4 1 4 3 2 5 6

1 6 6 6 4 2 5 5 5 3 1 4 4 1 3 4 2 3 2 3 2 1 5 6

Reduction The carbonyl group of an aldehyde or ketone is reduced to an -CHOH group by hydrogen in the presence of a transition-metal catalyst. Reduction of an aldehyde gives a primary alcohol. Reduction a ketone gives a secondary alcohol.

Reduction Reduction by NaBH4 does not affect a carbon-carbon double bond or an aromatic ring.

Tollens Benedict

Keto-Enol Tautomerism

"enolizable"

"enolizable"

"enolizable"

"enolizable"

"enolizable"

"enolizable"

"enolizable"

tautomers "enolizable"

?

?

H

H H H H

H H H H H H

H H H H H H

H H H H H H

enediol

H enediol

H enediol

H enediol

Carboxylic Acids

Carboxylic Acids In this chapter, we study carboxylic acids, another class of organic compounds containing the carbonyl group. The functional group of a carboxylic acid is a carboxyl group, which can be represented in any one of three ways.

Nomenclature IUPAC names For an acyclic carboxylic acid, take the longest carbon chain that contains the carboxyl group as the parent alkane. Drop the final -e from the name of the parent alkane and replace it by -oic acid. Number the chain beginning with the carbon of the carboxyl group. Because the carboxyl carbon is understood to be carbon 1, there is no need to give it a number.

Nomenclature In these examples, the common name is given in parentheses. An -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-.

Nomenclature To name a dicarboxylic acid, add the suffix -dioic acid to the name of the parent alkane that contains both carboxyl groups; thus, -ane becomes -anedioic acid. The numbers of the carboxyl carbons are not indicated because they can be only at the ends of the chain.

Nomenclature

Nomenclature For common names, use, the Greek letters alpha (a), beta (b), gamma (g), and so forth to locate substituents.

Physical Properties

Physical Properties Carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight.

[A–] [H3O+] [HA] larger Ka HA + H2O A– + H3O+ Ka = increased [H3O+] stronger acid

[A–] [H3O+] [HA] larger Ka HA + H2O A– + H3O+ Ka = increased [H3O+] stronger acid

[A–] [H3O+] [HA] larger Ka HA + H2O A– + H3O+ Ka = increased [H3O+] stronger acid

[A–] [H3O+] [HA] larger Ka HA + H2O A– + H3O+ Ka = increased [H3O+] stronger acid

RCOOH + H2O RCOO– + H3O+ [RCOOH] [RCOO–] [H3O+] Ka =

RCOOH + H2O RCOO– + H3O+ [RCOO–] [H3O+] Ka = [RCOOH]

HCl HOAc PhOH EtSH EtOH HOH Comparative acidities of 0.1 M aqueous solutions of representative acids HA Ka % ionized [H3O+], M pH HCl HOAc PhOH EtSH EtOH HOH ~1  107 ~100 ~0.1 1.00 1.8  10–5 1.3 1.3  10–3 2.88 3.3  10–10 0.0036 3.6  10–6 5.44 2.5  10–11 0.0016 1.6  10–6 5.80 1.3  10–16 0.0001 1.0  10–7 7.00 1.8  10–16 0.0001 1.0  10–7 7.00 acids > phenols ~ thiols > water ~ alcohols

Fatty Acids Table 18.3 The Most Abundant Fatty Acids in Animal Fats, Vegetable Oils, and Biological Membranes.

Fatty Acids Unsaturated fatty acids generally have lower melting points than their saturated counterparts.

Fatty Acids Saturated fatty acids are solids at room temperature. The regular nature of their hydrocarbon chains allows them to pack together in such a way as to maximize interactions (by London dispersion forces) between their chains.

Fatty Acids In contrast, all unsaturated fatty acids are liquids at room temperature because the cis double bonds interrupt the regular packing of their hydrocarbon chains.

Soaps

Soaps

Decarboxylation Decarboxylation: The loss of CO2 from a carboxyl group. Almost all carboxylic acids, when heated to a very high temperature, will undergo thermal decarboxylation. Most carboxylic acids, however, are resistant to moderate heat and melt and even boil without undergoing decarboxylation. An exception is any carboxylic acid that has a carbonyl group on the carbon b to the COOH group.

Decarboxylation Decarboxylation of a b-ketoacid. The mechanism of thermal decarboxylation involves (1) redistribution of electrons in a cyclic transition state followed by (2) keto-enol tautomerism.

Decarboxylation An important example of decarboxylation of a b-ketoacid in biochemistry occurs during the oxidation of foodstuffs in the tricarboxylic acid (TCA) cycle. Oxalosuccinic acid, one of the intermediates in this cycle, has a carbonyl group (in this case a ketone) b to one of its three carboxyl groups.