HOAÙ HOÏC HÖÕU CÔ Organic Chemistry CHÖÔNG 13 AMINES & HỢP CHẤT DIAZONI

GIÔÙI THIEÄU

 Alkylamine N attached to alkyl group  Arylamine N attached to aryl group  Primary, secondary, or tertiary determined by number of carbon atoms directly attached to nitrogen Classification of Amines

Amines  R-NH 2  Name the “R” group or groups with “-yl” endings  Add the word “amine”

Amines C H H N H H H Methyl amine C H H N C H H H H H Dimethyl amine

Naming Amines Methylamine Ethylamine Propylamine Aniline or aminobenzene Ethylmethylamine Methylpropylamine Dipropylamine

 Two IUPAC styles 1)analogous to alcohols: replace -e ending by -anamine 2)name alkyl group and attach -amine as a suffix Nomenclature of Primary Alkylamines (RNH 2 )

Examples: some primary alkylamines CH 3 CHCH 2 CH 2 CH 3 NH 2 (RNH 2 : one carbon directly attached to N) CH 3 CH 2 NH 2 NH 2 ethylamine or ethanamine cyclohexylamine or cyclohexanamine 1-methylbutylamine or 2-pentanamine

 Name as derivatives of aniline. Nomenclature of Primary Arylamines (ArNH 2 )

Examples: some primary arylamines (ArNH 2 : one carbon directly attached to N) p-fluoroaniline 5-bromo-2-ethylaniline NH 2 F Br CH 2 CH 3

Amino groups as substituents p-aminobenzaldehyde  amino groups rank below OH groups and higher oxidation states of carbon  in such cases name the amino group as a substituent NH 2 HCO HOCH 2 CH 2 NH 2 2-aminoethanol

 Name as N-substituted derivatives of parent primary amine.  (N is a locant-it is not alphabetized, but is treated the same way as a numerical locant)  Parent amine is one with longest carbon chain. Secondary and Tertiary Amines

Examples CH 3 NHCH 2 CH 3 N-methylethylamine NHCH 2 CH 3 NO 2 Cl 4-chloro-N-ethyl-3-nitroaniline CH 3 N N,N-dimethylcycloheptylamine

 A nitrogen with four substituents is positively charged and is named as a derivative of ammonium ion (NH 4 + ). Ammonium Salts CH 3 NH 3 + Cl– methylammonium chloride N CH 3 H CH 2 CH 3 + CF 3 CO 2 – N-ethyl-N-methylcyclopentylammonium trifluoroacetate

 When all four atoms attached to N are carbon, the ion is called a quaternary ammonium ion and salts that contain it are called quaternary ammonium salts. Ammonium Salts + CH 2 N CH 3 I – benzyltrimethylammonium iodide

CAÁU TAÏO VAØ LIEÂN KEÁT

147 pm 106° 112° Alkylamines

Most prominent feature is high electrostatic potential at nitrogen. Reactivity of nitrogen lone pair dominates properties of amines. Alkylamines

Compare geometry at N of methylamine, aniline, and formamide. sp 3 sp 2 Geometry at N  Pyramidal geometry at sp 3 - hybridized N in methylamine.  Planar geometry at sp 2 -hybridized N in formamide. C O NH 2 H C H H H

Compare geometry at N of methylamine, aniline, and formamide. sp 3 sp 2 Geometry at N  Pyramidal geometry at sp 3 - hybridized N in methylamine.  Planar geometry at sp 2 -hybridized N in formamide.

Angle that the C—N bond makes with bisector of H—N—H angle is a measure of geometry at N. sp 3 sp 2 Geometry at N ~125° 180°  Note: this is not the same as the H—N—H bond angle

Angle that the C—N bond makes with bisector of H—N—H angle is a measure of geometry at N. sp 3 sp 2 Geometry at N ~125° 180° 142.5°

Geometry at N in aniline is pyramidal; closer to methylamine than to formamide. Geometry at N 142.5°

142.5°  Hybridization of N in aniline lies between sp 3 and sp 2.  Lone pair of N can be delocalized into ring best if N is sp 2 and lone pair is in a p orbital.  Lone pair bound most strongly by N if pair is in an sp 3 orbital of N, rather than p.  Actual hybridization is a compromise that maximizes binding of lone pair.

Electrostatic Potential Maps of Aniline Nonplanar geometry at N. Region of highest negative potential is at N. Planar geometry at N. High negative potential shared by N and ring. Figure 22.3 (page 862)

Amines  IR spectrum of 1-butanamine (Fig 12.11)

Reduction to Amines  Lithium aluminum hydride reduces amides and nitriles to amines.  Nitriles and 1 amides reduce to 1 amines.  A 2 amide reduces to a 2 amine.  A 3 amide reduces to a 3 amine. =>

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Amines: Physical properties  Most amines up to 5 or 6 carbons are water soluble due to hydrogen bonding with the water molecule.

Amines: Physical properties-2  Amines have boiling points between alkanes and alcohols. They hydrogen bond but not as strongly as alcohols. Tertiary amines cannot hydrogen bond to each other and boil lower then 1 o or 2 o of similar molecular weight.  C 4 H 8 (58), bp 0 o C  C 3 H 7 NH 2 (59), bp 48 o C  C 3 H 7 OH (60), bp 97 o C

 Amines are more polar and have higher boiling points than alkanes; but are less polar and have lower boiling points than alcohols. Physical Properties CH 3 CH 2 CH 3 CH 3 CH 2 NH 2 CH 3 CH 2 OH dipole moment (  ): boiling point: 0 D 1.2 D 1.7 D -42°C17°C78°C

 Boiling points of isomeric amines decrease in going from primary to secondary to tertiary amines.  Primary amines have two hydrogens on N capable of being involved in intermolecular hydrogen bonding. Secondary amines have one. Tertiary amines cannot be involved in intermolecular hydrogen bonds. Physical Properties CH 3 CH 2 NHCH 3 CH 3 CH 2 CH 2 NH 2 (CH 3 ) 3 N boiling point: 50°C34°C3°C

TÍNH BASE

Reactions of Amines: Basicity  Amines are weak bases. They accept protons from water making solutions basic.

Reactions of Amines: Basicity

Reactions of Amines: Neutralization  Amines form salts by accepting a proton from strong mineral acids.  Converting amines to salts often makes insoluble amines soluble!!!!! Name amine salts by replacing the suffix – amine with ammonium and the name of the anion. E. g. propylammonium chloride

Reactions of Amine Salts: Neutralization  Amine salts revert to the amine (donate a proton) in strong base.

Amine Reactions: “Quats”  3 o amines react with alkyl chlorides to give quaternary ammonium salts which are very important in biochemistry.

“Quats” cont.  Benzalkonium chloride (Zephiran TM ) and choline are important examples.

Heterocyclic Amines  Heterocyclic amines have at least one nitrogen in the ring. MANY are physiologically active and many are critical in biochemistry.

Examples of Heterocyclic Amines

Examples of Heterocyclic Amines-2

Amides  Most amides are solids at room temperature due to internal hydrogen bonding.  They are not bases. A resonance structure shows why the N lone pair is unavailable to accept a proton.

Amide Names  Names are derived from the acid.  Remove –ic acid (common) or – oic acid (IUPAC) and replace with –amide.  Nitrogen substituents are prefixed to the name and indicated by N. ethanamide or acetamide N-methylpropanamide

Preparation of Amides  1 o and 2 o amines react with acid chlorides to give amides. The acid chloride transfers its acyl group to the N of the amine.

Preparation of Amides-2  1 o and 2 o amines react with acid anhydrides to give amides. E. g. with acetic anhydride.

Amino Acids and Proteins  An alpha amino acid is a carboxylic acid with an amino group on the carbon alpha to the carboxylic acid.  The alpha carbon also has an R group side chain except for glycine which has two Hs. Generic amino acid at physiological pH.  C

Peptides  A peptide is a polymer of about amino acids linked by the peptide(amide) bond. As the amino group and the carboxyl group link, water is lost.

Hydrolysis of Amides  a) Amides hydrolyze with acid to give the carboxylic acid and the amine salt.  b) Amides hydrolyze with base to give the carboxylic acid salt and the amine.

16.4 Amino Acids and Protein Synthesis   -amino acids are attached to transfer RNA molecules (t-RNA). The acyl group ( and the amino acid) are transferred to the nitrogen of another amino acid to form a peptide (amide) bond. Aminoacyl group from amino acid

16.5 Neurotransmitters  Neurotransmitters carry signals from a nerve cell to a target They can be excitatory or inhibitory. All contain nitrogen. catecholamines A deficiency in dopamine results in Parkinson’s disease. Too much is associated with schizophrenia. It is also associated with the “high” of drugs.

Neurotransmitters-cont.  Catecholamines-cont.  Epinephrine (adrenaline) and norepinephrine are involved in the fight or flight response.  Serotonin  A deficiency is associated with depression, bulemia and anorexia nervosa. It also affects pain perception, thermoregulation, and sleep.

Neurotransmitters-cont.  Histamine is released during an allergic response.  Benadryl is a typical antihistamine used for colds and other allergic responses.  Acetylcholine functions at the neuromuscular junction to cause muscles to contract.

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