Chapter 12 Alcohols, Thiols, and Ethers
Alcohols • Contain the –OH group as in R-OH. • Nomenclature of alcohols: • Find the longest chain of C’s, which also includes the –OH group. Change the –e at the end of the usual base name to –ol. • Number the chain so that the –OH group has the lowest number ALWAYS!!! • Name any other substituents using these numbers. • Cyclic alcohols are named as cycloalkanols. • Benzene ring with an OH is called Phenol.
Classification of Alcohols • Alcohols are classified as primary (1o), secondary (2o), or tertiary (3o) based on how many C’s are bonded to the C with the –OH group. • LEP #1 Primary – has one alkyl group Secondary – has two alkyl groups Tertiary – has three alkyl groups
Thiols • Contain the –SH group. • Are known as compound with strong odors. • CH3CH2 – SH = Ethane thiol, added to natural gas. • CH3CH2CH2 – SH = Propane thiol, onions.
Ethers • Contain an O atom between two alkyl groups. • Oxygen atom does have lone pairs and make them slightly polar. • Some ethers with halogens were commonly used as anesthetic agents.
Properties of Alcohols, Ethers • Alcohols have Hydrogen Bonding type forces with the –OH group. • This significantly increases their boiling points and solubility in water. • Ethers are only slightly polar and have lower boiling points and limited solubility.
Properties • Solubility of smaller alcohols like methanol and ethanol are said to be miscible. • As the number of C’s increases to three and four, they have a solubility limit. • By the time we get to six C’s, it is insoluble. CH3-CH2-CH2-CH2-CH2-CH2 - OH Non-polar carbon chain dominates
Properties • Environmental Issue – MTBE • Methyl-t-butyl ether or MTBE – once added to gasoline as an “oxygenate.” • Problem: it is slightly soluble in water and is not biodegradable.
Properties • Phenol is slightly soluble in water due to the fact that it is a weak acid.
Reactions of Alcohols • Depends on the classification (1o, 2o, or 3o) for some reactions. • Oxidation = removal of 2 H atoms OR the addition of an O atom. • Reduction = removal of an O atom OR the addition of 2 H atoms. • I will show the oxidation processes for each type of alcohol. Reduction reverses the process. • [O] = oxidizing agent (KMnO4, K2CrO4)
Reactions of Alcohols • Primary • Ex) CH3CH2OH • Secondary • Ex) CH3CHCH3 OH • Tertiary • Ex) (CH3)3-C-OH
Reactions of Thiols • Oxidation of two thiols produces something called a disulfide. • One amino acid contains this and determines whether you have straight or curly hair. • 2 CH3CH2-SH
Aldehydes and Ketones • Carbonyl group, C=O, is polar with a partial negative charge residing on the O atom. • In an aldehyde, the carbonyl group has one or more H atoms bonded to the C atom. • In a ketone, the carbonyl group has two alkyl groups. C=O d+ d-
Aldehydes • Naming these replaces the –e in the base name with -al. • Carbon #1 MUST be the carbonyl carbon. • Any other substituents are numbered according to this numbering.
Ketones • Naming these replaces the –e ending to –one. • Will need a number for position of carbonyl if five or more C’s are present. • Can also have cycloketones – then carbonyl group is C #1.
Properties • The boiling points of aldehydes and ketones are higher than those of alkanes and ethers of similar mass. • This is due to the polar carbonyl group. • However, their boiling points are less than those of the alcohols, because the alcohols have Hydrogen Bonding forces.
Properties • Aldehydes and Ketones with four or less Carbons are very soluble in water. • Solubility is less than that for similar number of C’s with alcohol group. • Larger ones are not soluble. • Oxidation of aldehydes and ketones is like that for the alcohol series.
Chirality • Some molecules have the exact same formula and connections, but differ in their spatial arrangements. • These are called stereoisomers and result from a chiral carbon.
Chirality • Decide whether the following objects would be chiral or achiral.
Chirality • When a C atom has four different groups bonded to it, it said to be chiral. • The mirror image is of this molecule is NOT the same. • Test = Not Superimposable. CH3 C H OH Cl
Chirality • Which molecules have chiral carbons?
Ch. 13 Carboxylic Acids, Esters, Amines, and Amides
Carboxylic Acids • Contains both the carbonyl group and the hydroxyl groups (-COOH). • Collectively, these two are called the carboxylic group. • The H atom on the hydroxyl group is acidic.
Carboxylic Acids • Naming: • Identify longest chain with the carboxylic group. • Carboxylic group carbon is C#1. • Any other substituents are numbered based on this carbon. • Aromatic carboxylic acid is called benzoic acid.
Properties • -OH group forms Hydrogen Bonds • Carbonyl group is also very polar. • Have higher boiling points than alcohols. • 1-propanol (bp = 97oC) or ethanoic acid (bp = 118oC) both have molar mass of 60. g/mol. • Acids form a dimer.
Properties • One to four carbon chain acids are very soluble in water. • For five or more carbon acids, they are only slightly soluble in water. • Carboxylic acids are weak acids. • The H atom on the –OH group can be donated to a a base. • RCOOH + H2O RCOO- + H3O+
Properties • A strong base can be used to neutralize a carboxylic acid to yield water and a salt. • RCOOH + NaOH RCOO-Na+ + H2O • Some of the “salts” are used as preservatives in food products. • Ex) Sodium propionate and sodium benzoate
Reactions • A carboxylic acid will react with an alcohol to form an ester. O O H+ CH3 C-OH + HO-CH3 H2O + CH3 C – O – CH3
Esters • Are the fragrances of fruits, flavorings, and perfumes.
Ester • A fat or oil is a tri-ester of glycerol and three fatty acids (long chain carboxylic acids). • This is the our vegetable oil in the biodiesel project. • In the presence of a strong base (NaOH), the ester will dissociate into the carboxylic acid salt and the alcohol. • The carboxylic acid can then be converted to a single ester with methanol.
Amines • Amines are derivatives of ammonia (NH3) • Each H atom of ammonia can be replaced by an alkyl group. • Amines are classified as 1o, 2o, and 3o based on how many H atoms are replaced. Trimethyl amine
Properties • Amines with at least one H atom bonded to N will have hydrogen Bonding forces. • Those with HB will have higher boiling points, but less than the alcohols. • Propanol, 97oC; Propyl amine, 48oC, and Trimethylamine, 3oC • Amines are weak bases and will react with water like NH3. • Amine salt = reacting an amine with a strong acid.
Alkaloids • Amines are commonly found in plants and may have biological effects. caffeine
Amides • The reaction of a carboxylic acid and an amine produces an amide – similar to ester reaction. O H O H heat CH3CH2 C–OH + H-N-CH3 H2O + CH3CH2-C-N-CH3 • If you have a di-carboxylic acid plus a di-alcohol OR di-amine, then you can make a condensation type polymer. • Ex) Terephthalic acid + Ethylene Glycol • Ex) Hexamethyldiamine + Hexanedioic Acid