Basic Organic Chemistry III

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Organic Chemistry Review:

Organic Chemistry Review Part II

Organic Reactions :

Organic Reactions Addition Elimination Substitution Rearrangement Condensation Esterification Hydrolysis Oxidation & Reductions Combustion

Addition Reactions:

Addition Reactions The components of an organic molecule A–B are added to the carbon atoms in a C = C bonds. Involve the conversion of a π bond into 2 σ bonds. General form: A + B → C

Addition Reactions:

Addition Reactions Symmetrical alkenes produce one product. Unsymmetrical alkenes produce racemic mixtures.

Addition Reactions:

Addition Reactions Alcohols are often produced by addition reactions. Initial attack by the π bond of an alkene on a H δ + of H 3 O + produces a carbocation. The carbocation then undergoes nucleophilic attack by a lone pair of electrons from H 2 O. This is followed by elimination of H + to form the alcohol.

Addition Reactions:

Addition Reactions

Addition Reactions:

Addition Reactions With symmetrical alkenes, addition of hydroxyl group produces one type of alcohol.

Addition Reactions :

Addition Reactions With unsymmetrical alkenes, a ddition of hydroxyl group produces different types of alcohols depending on the location of the double bond +

Addition Reactions:

Addition Reactions Formation of hemiketals & hemiacetals : Reactions between an acohol and either a ketone or aldehyde.

Elimination Reactions:

Elimination Reactions T he removal or “ elimination” of adjacent atoms from a molecule . Two σ bonds are lost, replaced by a new π bond. The dehydration reaction of alcohols to generate alkene proceeds by heating the alcohols in the presence of a strong acid, such as sulfuric or phosphoric acid, at high temperatures. 

Elimination Reactions:

Elimination Reactions The required range of reaction temperature decreases with increasing substitution of the hydroxyl carbon: 1° alcohols: 170° - 180°C 2° alcohols: 100°– 140 °C 3° alcohols: 25°– 80°C

Elimination Reactions:

Elimination Reactions If the reaction is not sufficiently heated, the alcohols do not produce alkenes , but they react with one another to form ethers (Williamson Ether Synthesis).

Elimination Reactions:

Elimination Reactions General form: A → B + C

Elimination Reactions:

Elimination Reactions 1 ⁰ Alcohols

Elimination Reactions:

Elimination Reactions 2 ⁰ Alcohols

Elimination Reactions:

Elimination Reactions In dehydration reactions of alcohols, hydride or alkyl shifts relocate the carbocation to a more stable position. The dehydrated products are a mixture of alkenes, with and without carbocation rearrangement.

Elimination Reactions:

Elimination Reactions Hydride or alkyl shifts are the result of hyperconjugation . The interaction between the filled orbitals of neighboring carbons and the singly occupied p orbital in the carbocation stabilizes the positive charge in carbocation . The tertiary cation is more stable than a secondary cation , which is more stable than a primary cation .

Elimination Reactions:

Elimination Reactions Hydride shift:

Elimination Reactions:

Elimination Reactions Alkyl shift:

Substitution Reactions:

Substitution Reactions Nucleophilic substitution reactions. An electronegative atom is replaced by another more electronegative atom, called a stronger nucleophile. The stronger nucleophile must possess a pair of electrons and have a greater affinity for the electropositive carbon atom than the original electronegative atom. A σ bond is replaced by another σ bond .

Substitution Reactions:

Substitution Reactions General form: A + B → C + D Non-polar reactions:

Substitution Reactions:

Substitution Reactions Polar reactions:

Rearrangement Reactions:

Rearrangement Reactions Are isomerisation reactions. An organic molecule changes structure. Constitutional change in carbon skeleton. Reaction may involve changes in bond type. General form: A → B

Rearrangement Reactions:

Rearrangement Reactions

Condensation Reactions:

Condensation Reactions Two molecules combine to form one single molecule with the loss of a small molecule . When this small molecule is water, it is known as a dehydration reaction. Other possible small molecules lost include hydrogen chloride , methanol, or acetic acid.

Condensation Reactions:

Condensation Reactions When two separate molecules react, their condensation is termed intermolecular. The condensation of two amino acids to form a peptide bond ( red ) with expulsion of water ( blue ).

Condensation Reactions:

Condensation Reactions When a condensation is performed between different parts of the same molecule, the reaction is termed intramolecular condensation. In some cases this leads to ring formation.

Condensation Reactions:

Condensation Reactions

Esterification Reactions:

Esterification Reactions Esters are obtained by refluxing a carboxylic acid with an alcohol in the presence of an acid catalyst . The reaction is driven to completion by using an excess of either the alcohol or the carboxylic acid, or by removing the water as it forms. Alcohol reactivity order :  CH 3 OH > 1 o > 2 o > 3 o (steric effects ).

Esterification Reactions :

Esterification Reactions A carboxylic acid and an alcohol react together under acidic conditions to form an ester and lose water.

Esterification Reactions:

Esterification Reactions Esters can also be made from other carboxylic acid derivatives, especially acyl halides and anhydrides, by reacting them with the appropriate alcohol in the presence of a weak base. If a compound contains both hydroxy - and carboxylic acid groups, then cyclic esters or lactones can form via an intramolecular reaction. Reactions that form 5- or 6-membered rings are particularly favorable.

Esterification Reactions:

Esterification Reactions Pericyclic esters

Hydrolysis :

Hydrolysis A reaction in which water is a reactant, and becomes part of the reaction product. A number of organic compounds undergo hydrolysis with water, such as amides, esters, halogenoalkanes and acyl halides.

Hydrolysis :

Hydrolysis Reactions require a catalyst. The catalyst is either an acid (H + ions) or alkali (OH - ions). Hydrolysis might involve refluxing in the presence of dilute hydrochloric acid or sodium hydroxide solution.

Hydrolysis:

Hydrolysis In the overall reaction, a bond in an organic molecule is broken. A water molecule also breaks into ions. The -OH group from water is added to one end of the organic molecule and the remaining H atom is added to the other.

Hydrolysis of an Ester::

Hydrolysis of an Ester: The addition of a strong acid, such as dilute hydrochloric acid, is required to free the carboxylic acid molecule. In the base-catalyzed, the carboxylic acid molecule loses a proton to a hydroxide ion .

Hydrolysis of Amides & Nitriles::

Hydrolysis of Amides & Nitriles: Amide acid catalyzed - HCl Nitrile acid catalyzed – HCl or H 2 SO 4

Hydrolysis of Halogenalkanes::

Hydrolysis of Halogenalkanes :

Hydrolysis of Aromatics:

Hydrolysis of Aromatics

Summary of Hydrolysis Reactions:

Summary of Hydrolysis Reactions The hydrolysis of a primary amide: RCONH 2 + H 2 O    →    RCOOH + NH 3 The hydrolysis of a secondary amide: RCONHR ' + H 2 O    →    RCOOH + R'NH 2

Summary of Hydrolysis Reactions:

Summary of Hydrolysis Reactions The hydrolysis of an ester: RCOOR ' + H 2 O    →    RCOOH + R'OH The hydrolysis of a halogenoalkane : RBr + H 2 O    →    ROH + H + + Br -

Reduction & Oxidation (REDOX) Reactions:

Reduction & Oxidation (REDOX) Reactions Oxidation States Oxidations Reductions

Definitions:

Definitions Oxidation-Reductio n reaction s: Involv e changes in oxidation state at one or more atoms. Can often be identified by changes in the number of oxygen atoms at a particular position in the hydrocarbon skeleton or in the number of bonds between carbon and oxygen at that position. It is not consider a n ox i d a t i o n or re d uc ti o n reaction: A d d i t i o n or l o s s of H + , H 2 O , HX .

Definitions:

Definitions Oxidation: T he oxidation state increases Lo ss of H 2 Loss of a C-H bond Ad d i t io n of O or O 2 Formation of a C-O bond or equivalent (C-Cl, C Ξ N, C-S) Ad d i t io n of X 2 ( h a l og e n s )

Definitions:

Definitions Reduc tion: The oxidation state decreases Ad d i t io n of H 2 or H - Formation of a C-H bond L o ss of O or O 2 Loss of a C-O bond or equivalent Lo ss of X 2 . An increase in the number of hydrogen atoms in a hydrocarbon is often an indication of a reduction.

Oxidation States:

Oxidation States Carbo n oxidatio n state s ar e assigne d o n th e basis of the electronegativit y o f attache d atoms. For each bond to a more electronegative atom give + 1. For each bond to a less electronegative atom (even H) give – 1. For each bond to carbon give 0.

Oxidation States:

Oxidation States

Oxidation States:

Oxidation States In nitrogen-containing compounds, the number of carbon–nitrogen bonds changes with the oxidation state of carbon.

Oxidation States:

Oxidation States

PowerPoint Presentation:

Assig n oxidatio n state s t o al l atom s i n the followin g structure : C H O C H C C O H H H H H H

PowerPoint Presentation:

Assig n oxidatio n state s t o al l atom s i n the followin g structure : -2 C + 1 H O +3 C H +1 C -2 -3 C -2 O + 1 H +1 H H H +1 H +1 H +1 +1 -2

Problem:

Identif y i f th e followin g reaction s are oxidation - reductio n reactions . Fo r an y tha t are , identif y th e atom s tha t are oxidized and reduced . B r I + N a I + N a B r + H 2 O H + K - O O + K Mn O 4 + Mn O 2 + H 2 O Pr ob le m

Problem:

Pr ob le m No , bot h B r an d I ar e mor e electronegativ e tha n C -2 + H 2 Yes , th e carbo n atom s ar e reduced , th e H 2 molecul e i s oxidized

Problem:

Pr ob le m

Summary of Oxidation States:

Summary of Oxidation States

REDOX Reactions of Alcohols:

REDOX Reactions of Alcohols A lc oh o l s can u n d er g o e i t h e r o x id at io n or r e d u c t io n t y pe reac ti o n s. O x i da ti on is a l os s of ele c t r o n s . R e d u c t io n is a g a in o f e l ec t r on s .

Oxidation of Alcohols:

O x i da ti on of A l c o h ol s 1⁰ and 2⁰ alcoho l s are e a s ily o x i di z ed by a var i e ty of re a g e n t s . T he m ost co m m on reag e nts u s ed: P y rid i n i um c h l o r o c h r o m ate (PCC) Po t a s s i um pe r m a n g a na t e T her m al de h y dr o g e n at io n

Oxidation of Alcohols:

O x i da ti on of A l c o h ol s T he m ost co m m on reag e nt u s ed f or o x i d a ti on of 2 ⁰ alcoho l s t o k et on e s i s c h r o m ic acid, H 2 Cr O 4 . 3 ⁰ alcohols a re r e s i s t a n t t o o xi da ti on bec au se t h e y ha v e no h y dr o g e n a to m s attac h ed to t h e o x y g e n be a r i ng ca r b o n ( carb i n o l ca r b on ).

Oxidation of 1⁰ Alcohols:

O x i da ti on of 1⁰ A l c o h ol s 1⁰ alc o ho ls a r e ea s ily oxidiz e d ju st l i ke 2⁰ alco h o l s. The p r o d u c t o f ox i da ti on is a n a ld e h y de. Th e a l d e h y de is e a s ily ox i di z ed to a n a c i d as a result of “ove r - o x i d a t io n”. A reage n t th at s e le c t iv e ly o x id iz e s a 1⁰ alc o ho l t o an a l d e h y de i s p y rid i n i um c h l o r o c h r o m ate , PCC .

Oxidation of 2⁰ Alcohols:

O x i da ti on of 2⁰ A l c o h ol s T he al co h o l a nd c h r o m ic acid p ro du c e a c hr o m ate e s ter, wh i c h th e n r e d uc ti vely el i m in a t e s t he Cr s p ec i e s . T he Cr i s r e d u c ed ( V I  I V ), the a lc oh ol i s o x id iz e d to a ketone.

Summary of Oxidation of Alcohols:

Summary of O x i da ti on of A l c o h ol s

Reduction of Alcohols:

Reducti on of A l c o h ol s N or m ally an a l c o h o l ca n n o t b e d ire ct ly red u c e d t o a n a l k a ne i n o ne s t e p . T he – O H g ro up is a p oor le a v i n g g r ou p and h y dri d e d i sp lace m e n t cannot happen. Instead, the h y dr o x y l gr ou p i s e a s i ly conv e rt e d i n t o ot her gr ou ps t h a t are better l e a v i n g g r ou ps, a nd a l low reac t i on t o move forward.

Reduction of Alcohols:

Reduction of Alcohols Commons reagents are t os y l c h l o r id e and lithium aluminum hydride ( L i A l H 4 ). The reaction i nv o l v e s t h e for m at i on of a t os y l ate . The t os y la t es can undergo either substitution or elimination reactions.

Reduction of Alcohols:

Reduction of Alcohols The t os y la t e re d u c es to c y cloh e x a ne v ery eas i l y with lithium aluminum hydride .

Reduction of Carboxylic Acids:

Reduction of Carboxylic Acids Carboxylic acids are reduced to 1 ⁰ alcohols.

Reduction of Esters:

Reduction of Esters Esters are reduced to 1 ⁰ alcohols.

Reduction of Amides:

Reduction of Amides Amides are reduced to 1 ⁰, 2 ⁰, or 3 ⁰ amines.

Reduction of Aldehydes:

Reduction of Aldehydes Aldehydes and ketones are reduced to 1 ⁰ and 2 ⁰ alcohols respectively.

Summary REDOX Reactions:

Summary REDOX Reactions

Combustion Reactions:

Combustion Reactions The reaction of an organic molecule with oxygen to form carbon dioxide, heat/energy and water.

Combustion Reactions:

Combustion Reactions Alkanes: Alkenes: Alcohols

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