Orgo Exam 3 Review
Orgo Exam 3 Review CHEM 225
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This 14 page Study Guide was uploaded by MelLem on Wednesday April 6, 2016. The Study Guide belongs to CHEM 225 at Simmons College taught by Professor gurney in Spring 2016. Since its upload, it has received 64 views. For similar materials see Organic chemistry 2 in Chemistry at Simmons College.
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CHEM 225 Organic Chemistry II UNIT III – Carboxylic Acids and Carboxylic Acid Derivatives Lectures 11-12 Chapter 21 – carboxylic acids and their derivatives 21.1 – Introduction to carboxylic acids - Carboxylic Acids – compounds with a R-COOH moiety. These compounds are abundant in nature and are responsible for some familiar odors. o CH3COOH – acetic Acid – responsible for the smell of vinegar Found in a wide range of pharmaceutical products that are used to treat a variety of conditions. o For example – acetylsalicylic acid is found in aspirin. Vinyl acetate is a derivative of acetic acid, therefore said to be a carboxylic acid derivative 21.2 – Nomenclature of Carboxylic Acids -Monocarboxylic Acids Contain only one carboxylic acid moiety. Named with the suffic -–ic acid. The parent is the longest chain that includes the carbon atom of the carboxylic acid moiety. When a carboxylic acid moiety is connected to a ring, the compound will be named as an alkane carboxylic acid. Common carboxylic acids to memorize Formic acid Acetic Acid Propionic acid Butyric acid Benzoic acid -Diacids Compounds containing 2 carboxylic acid moieties Named with the suffix –dioic acid 21.3 – Structure and Properties of –COOH -Structure Carbon atom of the carboxylic acid moiety is sp2 hybridized and exhibits trigonal planar geometry. Bond angles are ~120 degrees Carboxylic acids can form 2 hydrogen bonding interactions allowing molecules to associate with each other in pairs. The hydrogen bonding interactions explain why carboxylic acids have high boiling points. -Acidity of Carboxylic Acids Carboxylic acids exhibit mildly acidic protons. Treatment of a carboxylic acid with a strong base yields a carboxylate salt. Carboxylate salts are ionic, therefore more soluble in water than their corresponding carboxylic acids. Carboxylate ions are named by replacing the suffix –ic acid with the suffix -ate. When dissolved in H2O an equilibrium is established in which both the carboxylic acid and the carboxylate ion are both present. In most cases, the equilibrium favors the carboxylic acid 21.4 Preparation of Carboxylic Acids Review of carboxylic acid preparation (Table 21.1 in Klein) 1. Oxidative Cleavage of Alkynes a. Reagents 1) O3 2) H2O b. Cleaves the triple bond and forms 2 carboxylic acids 2. Oxidation of Primary Alcohols a. Reagents Na2Cr2O7 / H2SO4, H2O b. Other strong oxidizing agents can be used as well c. Oxidizes from Oxidation level of  to  3. Oxidation of Alkyl benzenes a. Reagents Na2Cr2O7 / H2SO4, H2O b. Any alkyl group on an aromatic ring WILL be completely oxidized ti give benzoic acid (benzylic position much have atleast 1 H proton) Hydrolysis of Nitriles When treated with aqueous acid, a nitrile (a compound with a cyano group) can be converted to a carboxylic acic. This process of called Hydrolysis It is a 2 step RXN for converting an alkyl halide into a carboxylic acid. Carboxylation of Grignard Reagents Carboxylic acids can also be prepared by treating a Grignard reagent with CO2. 21.5 – Reactions of Carboxylic Acids Carboxylic acids are reduced to alcohols upon treatment with LAH (Lithium Aluminum hydride) They can also be reduced with Borane (BH3) Borane reacts selectively with the carboxylic acid moiety in the presence of another carbonyl group. BH3 * TFH Primary alcohol. 21.7 Introduction to carboxylic acid derivatives Classes of carboxylic acid derivatives 1. Reduction – those that change the oxidation state of the compound 2. No [o] level change – those that do not change the oxidation state of the compound. Replacement of the OH groups with a different group (Z – which is a heteroatom) does not involve a change in the oxidation state if Z is a heteroatom (Cl, O, N, F, ect. Anything but C and H) Compounds of this type are carboxylic acid derivatives Types of Carboxylic Acid derivatives 1. Acid Halides 2. Acid Anhydride 3. Ester 4. Amide 5. Nitrile ( 1 is the most reactive, 5 being least reactive) Carboxylic acid derivatives in Nature Acid halides and anhydrides DO NOT occur (commonly) naturally in nature due to their high reactivity. In contrast, Esters, are more stable and are abundant in nature. Amides are abundant in living organisms (proteins are comprised of repeating amide linkages) Naming Acid Halides Acid halides are named as derivatives of carboxylic acids by replacing the suffix –ic acid with the suffix –yl halide. When an acid halide moiety is connected to a ring, the suffic “carboxylic acid” is replaced with “carbonyl Halide” Naming Anhydrides Anhydrides are named as derivatives of carboxylic acids by replacing the suffix –acid with –anhydride Unsymmetrical anhydrides are prepared from 2 different carboxylic acids o They are named by indicating both acid alphabetically followed by the suffix anhydride Naming Esters Esters are named as derivatives of carboxylic acids by replacing the suffix –oic acid with the suffix –ate. What is attached to the C-O- is named first (the R group attached to O). Orgo 225 Lecture 13 21.12 Preparation and Reactions of Amides Preparation of amides Amides can be prepared from any of the carboxylic acid derivatives Most efficiently prepared from acid chlorides Reactions Acid Catalyzed Hydrolysis of Amides Amides can be hydrolyzed to give carboxylic acids Base catalyzed Hydrolysis of Amides Amides can also be hydrolyzed when heated in basic aqueous conditions (this process is very slow) Reduction of Amides When treated with LAH, amides are converted to amides The carbonyl group is completely removed 21.13 Preparation and Reactions of Nitriles Preparation of nitriles via SN2 reaction Nitriles can be prepared by treating an alkyl halide with a cyanide ion Preparation of nitriles from amides Nitriles can be prepared via dehydration of an amide Hydrolysis of nitriles Occurs in aqueous acid conditions Nitriles are hydrolyzed to amides then further hydrolyzed to carboxylic acids Reactions between nitriles and Grignard reagents A ketone is obtained when a nitrile is treated with a Grignard reagent Grignard attacks the nitrile – the resulting anion is treated with aqueous acid to give an imine then hydrolyzed to a ketone Reduction of nitriles Nitriles are reduced to amines when treated with LAH 21.14 Synthesis Strategies C-C bond forming reactions c-c bond forming reactions in which the F.G remains the same: 1) Xs RMgBr 2) H2O R2CuLi 1) RMgBr 2) H3O+ In class lecture 13 summary: o Nucleophiles (Nu) – frequently negative, but sometimes not. o Pyridine is not a nucleophile because it wont attack an electrophilic carbon due to sterics since N is in the Ring. New Rxn: o Hydrolysis of amides Saponification – hydrolysis of amides in basic conditions 1) NaOH 2) H3O+ Under Acidic Conditions – H3O+ o Reduction of Amide LAH Knocks out the carbonyl group. o Nitriles SN2 rxn NaCN o Dehydration SOCl2 Gives you the product + H2O o Reduction with LAH From oxidation level 3 1 because LAH is a strong reducer Reduces nitriles down to amines Carboxylic acids are the only acid derivative that don’t get attacked at the carbonyl. Anytime you start with a carboxylic acids, react with SOCl2 to make an acid chloride It will never be wrong to go to an acid chloride then down to a lower reactivity. LIPIDS 26.1 Introduction to Lipids and Lipid Chemistry Lipids – defined by the physical property, solubility. Complex lipids – lipids that are readily able to undergo hydrolysis in aqueous acid Lipids are either: Complex Lipids (can be hydrolyzed) o Waxes o Phospholipids o Triglycerides Simple Lipids (cannot be hydrolyzed) o Steroids o Prostaglandins o Terpenes All three of the complex lipids contain ester moieties – rendering them easily hydrolyzed. They also contain long hydro carbon chains – making them soluble in organic solvents. 26.3 Triglycerides o Triglycerides are triesters formed from glycerol and 3 long chain carboxylic acids (commonly known as fatty acids) o A triglyceride is said to contain 3 fatty acid residues o (They are used by mammals and plants for longer term energy storage) Lecture 14 In Class summary Lipids – be able to distinguish between saturated and unsaturated fats, soaps, steroids, waxes, phospholipids, recognize fat vs H2O soluble vitamins. Be able to draw a typical triglyceride Know how to make a soap, and how soap works. Know triacyl glycerides Hydrolysis under basic and acidic conditions: Under basic conditions = saponification Know how to draw amino acids with the side chain given, be able to classify them as nonpolar, polar neutral, polar basic, or polar acidic. PI – isoelectric point when the zwitter ion exists (neutral overall – but has charges) Be able to draw an amino acid in varying pH’s At a lower pH, the N has a + charge and is NH3 Neutral but still charged – N has a + charge, CO- charge At pH higher than the PI (NH2) and CO has a – charge Chemistry 225:Organic Chemistry Review Problems for unit III 1) Place the following compounds in order of increasing reactivity to hydrolysis: a) ester b) acid chloride c) ketone d) amide e) anhydride 2) Rank the following compounds in order of increasing acidity. a) trifluoroacetic acid b) tribromoacetic acid c) pnitrophenol d) pmethoxybenzoic acid 3) Draw structures corresponding to these IUPAC names: a) 2hexen4ynoic acid b) heptanedioic acid c) 4ethyl2propyloctanoic acid d) cyclohexyl ethanoate e) 2,2dimethyl hexanamide f) ethyl acetate g) benzoyl chloride h) ethanoic butanoic anhydride 4) Rank the following para substituted methyl benzoates in increasing reactivity to hydrolysis: O O O O CH3O Br O2N H OCH 3 OCH3 OCH 3 OCH3 5) Which compound would you expect to react faster with nucleophiles? O O CH3O Cl (CH3 2N Cl 6) Identify the monomeric units in the following polymer: O O O O O n 7) Rank the following compounds in order of increasing basicity: a) EtNH 2 b) PhNH 2 c) Et2NH d) Ph 2H e) Et3NH 8) Synthesize the products shown below by starting with ethanol, isopropanol and sodium cyanide as your only source of carbon. START WITH SYNTHESIZE: O OH O OH OH HO CO 2 NaCN O 9) Propose a mechanism for the following reaction. O H+ OH OH O O 10) Synthesize the following products: O O O O N b) O c) a) O from alcohol from any acyclic from alcohol with 3 carbons or amine with starting material 4 or fewer carbons or less d) ethyl propanoate from bromoethane 11) Fill in the structures of the missing intermediates or reagents in each of the following reactions. j) methyl benzoate reacting with DIBAH gives what product? k) pentanoyl chloride reacting with Lithium tri tbutoxy aluminium hydride: l) 1bromobutane and sodium azide followed by LAH: Lipids and proteins review problems: 1) Which of the following molecules will readily dissolve in water? a) glucose b) valine c) cholesterol d) sodium hexanoate e) ethylamine f) benzene g) octanol h) octanoic acid 2) Which of the following templates contains a steroid backbone? A B C D 3) Show the products you would expect to obtain from reaction of glyceryl trioleate with excess of the following reagents? + + a) NaOH/H O 2 b) LAH; H c) H /Pd2 d) CH M3Br, H O O (CH2 7CH=CH(C2 7 3H O (CH2 7CH=CH(C2 7 3H O O (CH2 7CH=CH(C2 7 3H O glyceryl trioleate 4) For the mixture of amino acids indicated, predict the direction of migration of each component. (toward cathode (+) or anode ()) a) Valine, Glutamine, Histidine at pH 7.6 (pI of val = 6.0; glu = 5.7; his = 7.6) b) Glycine, Phenylalanine, Serine at pH 5.7 (pI of gly = 6.0; phe = 5.9; ser = 5.7) c) Glycine, Phenylalanine, Serine at pH 6.0 5) a)Draw the full structures for the following peptide with correct stereochemistry: ValPheCysAla b) Draw the two fragments that will be produced after treating the above tetrapeptide with Edman degradation conditions. c) Draw the products after treating the peptide with Sanger Reagent followed by complete hydrolysis. 6) Which amide bonds in the following polypeptide are cleaved by trypsin? by chymotrypsin? PheLeuMetLysTyrAspGlyGlyArgValIleProTyr 7) A new peptide (P1) with potent anticonvulsive activity has been discovered. Hydrolysis of the peptide and analysis by HPLC indicates the presence of 5 different amino acids in equimolar amounts: Ala (pI = 6.0); Gly (pI = 6.0); Val (pI = 6.0); Phe (pI = 5.9); Glu (pI = 3.2). Reaction of P1 with Sanger Reagent followed by hydrolysis produced the following 2,4 dinitroanilido compound: NO 2 NO 2 NHCH C2OH When P1 is subjected to chymotrypsin, 2 fragments are produced: P2 and P3. Fragment P3 has pI of 3.2. Additionally, incubation with carboxypeptidase also produced P3 as the first amino acid to appear. Edman degradation of P2 produced P4. Edman degradation of P4 produced phenylthiohydantoin derivative of valine. a) what is the Nterminal amino acid of P1? b) what is the C terminal amino acid of P1? c) write the amino acid sequence of P1. 8) Synthesize the following artificial amino acid and describe in detail how you would resolve the racemic mixture. NH 2 COOH 9) Starting with the naturally occurring amino acids, Lphenylalanine, Lvaline, and Lmethionine, synthesize the following tripeptide. Be sure to use protecting groups where appropriate. PheValMet Chem 225: Answers to Review Problems for Unit 3 1) c<d<a<e<b (most reactive) 2) c<d<b<a (most acidic) 4) a<d<b<c (most reactive) 5) compound A will be more reactive than B j) benzaldehyde k) pentaldehyde l) butanamine For answers to lipids/proteins, open up another answer file in wiki.
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