Presentation on theme: "March 3oth , 2011 Goals for the day:"— Presentation transcript:
1March 3oth , 2011 Goals for the day: Naming AminesPhysical Properties of AminesAmine reactions* Conversion of an alkyl halide* Gabriel Synthesis* Hoffman Elimination4) IR/NMR of Amines5) Multiple Choice Questions…
2Chapter 24 Amines NH3 ammonia methyl amine isopropyl methyl amine Name the groups (up to 3) that are attached.Di & tri prefixes are used if groups are the sameNH3 ammoniamethyl amineisopropyl methyl amine
3Degree of substitution… Substitution on the nitrogen is important …The number of carbons directly attached to the nitrogen is whatYou want to look atPrimary secondary tertiary
524.2 Properties of Amines Bonding to N is similar to that in ammonia N is sp3-hybridizedC–N–C bond angles are close to 109° tetrahedral value
6Amines Form H-BondsAmines with fewer than five carbons are water-solublePrimary and secondary amines form hydrogen bonds, increasing their boiling points
724.3 Basicity of AminesThe lone pair of electrons on nitrogen makes amines basic and nucleophilicThey react with acids to form acid–base salts and they react with electrophiles
8AmidesAmides (RCONH2) in general are not proton acceptors except in very strong acidThe C=O group is strongly electron-withdrawing, making the N a very weak baseAddition of a proton occurs on O but this destroys the double bond character of C=O as a requirement of stabilization by N=
9SN2 Reactions of Alkyl Halides Ammonia and other amines are good nucleophiles
10Problem: Uncontrolled Multiple Alkylation (i. e Problem: Uncontrolled Multiple Alkylation (i.e. can’t stop the reaction! ).Primary, secondary, and tertiary amines all have similar reactivity, the initially formed monoalkylated substance undergoes further reaction to yield a mixture of products
11Gabriel Synthesis of Primary Amines A phthalimide alkylation for preparing a primary amine from an alkyl halideThe N-H in imides (–CONHCO–) can be removed by KOH followed by alkylation and hydrolysis
12Hofmann Elimination Converts amines into alkenes NH2 is very a poor leaving group so it is converted to an alkylammonium ion, which is a good leaving group
13The Elimination StepExchanges hydroxide ion for iodide ion in the quaternary ammonium salt, thus providing the base necessary to cause elimination
14Orientation in Hofmann Elimination We would expect that the more highly substituted alkene product predominates in the E2 reaction of an alkyl halide (Zaitsev's rule)However, the less highly substituted alkene predominates in the Hofmann elimination due to the large size of the trialkylamine leaving groupThe base must abstract a hydrogen from the most sterically accessible, least hindered position
1724.10 Spectroscopy of Amines -Infrared Infrared Spectroscopy:Characteristic N–H stretching absorptions 3300 to 3500 cm1Amine absorption bands are sharper and less intense than hydroxyl bandsProtonated amines show an ammonium band in the range 2200 to 3000 cm1
19NMRHydrogens on a carbon attached to an oxygen (or nitrogen) are around 3-4 ppm.Hydrogens on a carbon next to a carbonyl are around 2 ppm.
20Putting it all together… Reactions for exam three are on the following pages.Note that reactions with a *** you need to know the mechanism…
21Oxidation of primary alcohols Reagents can be H2CrO4, CrO3, [O], PCCPrimary alcohols can be oxidized to carboxylic acidsReaction of CO2 with a Grignard reagent ***
22Reactions that Carboxylic Acids do… React with bases… ***Makes acid halides(do the same reactions asacids, but are faster)…Reduces to a primary alcohol(goes through an aldehyde)…
23Two main Carboxylic Acid Reactions (need to be acid or base catalyzed)… Esterification…***Important in fatsAmide formation…***Important in proteins (amide bonds)Note: You will need to know all of the mechanisms, but the good newsis that they are very similar! (We will review them with the acid derivatives…)
24Reactions of Acid Derivatives… Ester and amide formation using an acid halide
25More reactions of Acid Derivatives… X = halogen, OR, or NHRHydrolysis ***(very important for bothesters and amides)Reduction using LAH(gives an amine if startingwith an amide)Goes through a ketone ***
40Chloroacetic acid is a stronger acid than acetic acid Chloroacetic acid is a stronger acid than acetic acid. Which is the best explanation?More resonance structures can be drawn for chloroacetic acid than for acetic acid.More resonance structures can be drawn for chloroacetate ion than for acetate ion.Because of its high electronegativity, chlorine is able to donate electrons to the chloroacetate ion by the inductive effect, thereby stabilizing this ion.Because of its high electronegativity, chlorine is able to withdraw electrons from the chloroacetate ion by the inductive effect, thereby stabilizing this ion.Chlorine is larger than hydrogen and can better hold a negative charge.
41AnswerBecause of its high electronegativity, chlorine is able to withdraw electrons from the chloroacetate ion by the inductive effect, thereby stabilizing this ion.
42p-Chlorobenzoic acid is more acidic than p-methylbenzoic acid. TrueFalse
48Which of the statements is true concerning the following two carboxylic acid derivatives? Only molecule A can be hydrolyzed.Only molecule B can be hydrolyzed.Both molecules can be hydrolyzed, but A will react faster than B.Both molecules can be hydrolyzed, but B will react faster than A.A and B can be hydrolyzed at roughly the same rate.
49AnswerBoth molecules can be hydrolyzed, but B will react faster than A.
50Predict the outcome of the following reaction. 188.8.131.52.5.12345
52Which of the following steps occurs first in the mechanism of Fischer esterification? attack of the nucleophile on the carbonyl carbonprotonation of the carbonyl oxygenloss of water from the tetrahedral carbonyl addition intermediateprotonation of the alcohol oxygenformation of the tetrahedral carbonyl addition intermediate
60Which of the following will occur when the following optically active compound is placed in dilute acid?It will form an acetal.It will form a diol.It will become an alcohol.It will lose its optical activity.none of these
70Which of the following statements explains why the following aldehyde will not undergo an aldol reaction with itself?The benzene ring makes the carbonyl group unreactive towards aldol reactions.A carbonyl group must be connected to two alkyl groups in order to undergo an aldol reaction.The molecule does not possess any hydrogens α to the carbonyl group.Electrophilic aromatic substitution competes favorably with the aldol reaction.Nucleophilic acyl substitution competes favorably with the aldol reaction.
71AnswerThe molecule does not possess any hydrogens α to the carbonyl group.
72Predict the aldol reaction product of the following ketone. 184.108.40.206.5.12345
82What type of reaction has occurred in the above biological process? Claisen condensationaldol reactionnucleophilic acyl substitutionβ-eliminationboth Claisen condensation and nucleophilic acyl substitution
88The major alkaloid present in tobacco leaves is nicotine, whose structure is shown below. Which will be the major ammonium ion formed when nicotine is treated with one equivalent of a strong acid?1.2.12
94Which of the following statements is true regarding the following two molecules? Both A and B are aromatic.Both A and B are aliphatic amines.A is more basic than B.B is more basic than A.Both A and B are planar molecules.