Organic Chemistry I: Reactions And Overview - Sites.tufts.edu
Organic Chemistry I: Reactions and OverviewAndrew RosenEditor: Raghav MalikJanuary 13, 2013ContentsI Library of Synthetic Reactions3II Organic Trends and Essentials41 The Basics: Bonding and Molecular Structure41.1Resonance Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Families of Carbon Compounds42.1Strength of London Dispersion Forces (Polarizability)2.2Degree of Unsaturation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 An Introduction to Organic Reactions and Their Mechanisms3.1Comparing Acid Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Nomenclature and Conformations of Alkanes and Cycloalkanes4.14Ring Flipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Stereochemistry445555.1Naming Enantiomers via the -R and -S System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55.2Stereochemistry Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66 Ionic Reactions - Overview66.1General Nucleophilic Substitution Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66.2Carbocation Stability66.3Factors A ecting the Rates of6.4Elimination Reactions6.5Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SN 1andSN 2Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77 Alkenes and Alkynes I - Overview87.1The E-Z System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87.2Relative Stabilities of Alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87.3Factors A ecting Elimination Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87.4Acid-Catalyzed Dehydration of Alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
III Reaction Mechanisms98 Ionic Reactions - Mechanisms98.1The8.2The8.38.4SN 2SN 1Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10The E2 Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10The E1 Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119 Alkenes and Alkynes I - Mechanisms119.1Acid-Catalyzed Dehydration of Secondary or Tertiary Alcohols: An E1 Reaction. . . . . . . . . . . . . . . .119.2Acid-Catalyzed Dehydration of Primary Alcohols: An E2 Reaction . . . . . . . . . . . . . . . . . . . . . . . .129.3Synthesis of Alkynes from Vic-Dihalides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129.4Substitution of the Acetylenic Hydrogen Atom of a Terminal Alkyne . . . . . . . . . . . . . . . . . . . . . . .129.5Deprotonation Reagents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129.6Hydrogenation13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Alkenes and Alkynes II - Mechanisms10.1 Addition ofH Xto an Alkene13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.2 Acid-Catalyzed Hydration of an Alkene13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1310.3 Mercuration-Demercuration and Hydroboration-Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1310.4 Summary ofH XandH OHAdditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.5 Electrophilic Addition of Bromine and Chlorine to Alkenes10.6 Halohydrin Formation from an Alkene14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1510.7 Oxidative Cleavage of Alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.8OsO4Reaction14. . . . . . . . . . . . . . . . . . . . . . . . . . . .15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1510.9 Summary for Dihalide, Dihydroxy, and Carbene Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1610.10 Electrophilic Addition of Bromine and Chlorine to Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . .1610.11 Addition of Hydrogen Halides to Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1610.12 Oxidative Cleavage of Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1611 Alcohols and Ethers - Mechanisms11.1 Alcohols withH X . . . . . .PBr3 or SOCl216. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1711.3 Leaving Group Derivatives of Alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1711.2 Alcohols with11.4 ConvertingOHtoLG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1711.5 Synthesis of Ethers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Summary1711.6 Protecting Groups18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11.7 Ether Reactions Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1811.8 Epoxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1811.9 Epoxide Reaction Summary with Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1912 Alcohols from Carbonyl Compounds - Mechanisms1912.1 Alcohols by Reduction of Carbonyl Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1912.2 Oxidation of Alcohols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1912.3 Alcohols from Grignard Reagents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1913 Radical Reactions - Mechanisms2013.1 Bromination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2013.2 Chlorination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202
Part ILibrary of Synthetic Reactions 1 Note that this is a partial list of reactions1 Graphicsare obtained mostly from Stony Brook University CHE 327 PowerPoint slides and Organic Chemistry , 10th Edition by Solomonsand Fryhle.3
Part IIOrganic Trends and Essentials1The Basics: Bonding and Molecular Structure1.1 Resonance Stability1. The more covalent bonds a structure has, the more stable it is2. Charge separation (formal charges) decreases stability3. Negative charges on the more electronegative elements and positive charges on the more electropositive elements are2more favorable2Families of Carbon Compounds2.1 Strength of London Dispersion Forces (Polarizability)1. Large atoms are easily polarizable and small atoms are not2. Atoms with unshared electron pairs are more polarizable than atoms with only bonding pairs3. Molecules that are longer and atter ( long chains ) have more surface area and thus have larger dispersion forces whenother factors are similar2.2 Degree of Unsaturation A degree of unsaturation is either a Formula:2C 2 N H X2πbond or a ring structurewhere the variables are the number of carbons (C), nitrogens (N), hydrogens (H), andhalogens (X)3An Introduction to Organic Reactions and Their Mechanisms3.1 Comparing Acid Strengths3Factors A ecting Acidity (in decreasing signi cance) : ARIO1. Atom2. Resonance Stabilization3. Induction E ect4. Orbital (s character)2 Forthe purposes of drawing all resonance structures, it is not considered a violation of the octet rule if a second-row element, like carbon, hasfewer than an octet. It is less likely but still imperative to draw.3 Thisgeneral trend is not always perfectly applicable. However, it is usually a fairly good indicator.4
ARIO Explained: Atom: Look at what atom the charge is on for the conjugate base. For atoms in the same row, we consider electronegativity. The further to the right on the periodic table an atomis, the more electronegative it is. If a conjugate base's negative charge is on a more electronegative atom, it ismore stable, and thus the parent acid is stronger. For atoms in the same column, we consider an atom's ability to stabilize a charge.The further down on theperiodic table an atom is, the better it is at stabilizing a charge. If a conjugate base's negative charge is morestabilized on an atom further down a group, it is a more stable molecule, and thus the parent acid is stronger. Resonance Stabilization: Look at resonance structures. The more distributed the charge of the conjugate base is, thestronger the parent acid is. Inductive E ect: Look for inductive e ect. If there are many electronegative atoms near the conjugate base's negativecharge, electron density is pulled toward these atoms. This creates more stable anions and thus more acidic parentmolecules. However, if there are many alkyl groups, this is a process called hyperconjugation, and the parent acid isactually less stable. Orbital: Look at the orbital where the negative charge for the conjugate base is. Morescharacter of a bond withhydrogen makes it more acidic.4Nomenclature and Conformations of Alkanes and Cycloalkanes4.1 Ring Flipping The axial groups become equatorial and vice versa When doing a ring ip, whether a group is up or down does not change Chair Conformation 1:Chair Conformation 2 (after ring ip): When performing a chair ip, each atom is rotated one spot in the clockwise direction A molecule is more stable when steric hindrance is minimized and bulky substituents are equatorial as opposed to axial5Stereochemistry5.1 Naming Enantiomers via the -R and -S System1. Each of the four groups attached to the chirality center is assigned a priority of 1, 2, 3, or 4. Priority is assigned on thebasis of the atomic number of the atom that is directly attached to the chirality center. The group with the highestatomic number gets the highest priority and vice versa.2. When a priority cannot be assigned on the basis of atomic number of the atoms, then the next set of atoms in theunassigned groups is examined. This process is continued until a decision can be made at the rst point of di erence.5
(a) Step 1:Step 2:3. If the 4th atom is a dashed wedge (downward): Analyze if the numbers (1 2 3 4)go clockwise or counterclock-wise. Clockwise indicates that the molecule is R, while counterclockwise indicates the molecule is S. 4. If the 4th atom is a solid wedge (upward): Analyze this intermediate molecule to see if the numbers go clockwise orcounterclockwise. Clockwise indicates that the original molecule is S, while counterclockwise indicates the moleculeis R. 5.2 Stereochemistry Examples6Ionic Reactions - Overview6.1 General Nucleophilic Substitution Reactions A deprotonation step is required to complete the reaction when the nucelophile was a neutral atom that bore a proton4Example showing deprotonation :6.2 Carbocation Stability Order of Carbocation Stability:3 2 1 Methyl6.3 Factors A ecting the Rates of SN 1 and SN 2 Reactions Simple alkyl halidesMethyl4 Deprotonationshow the following trend for order of reactivity inSN 2reactions: primary secondary (tertiary-unreactive)is normally seen asH3 O in water, but when there is a di erent solvent in excess it will be di erent6
The rates ofSN 2reactions (notSN 1)depend on both the concentration and identity of the attacking nucleophile In a selection of nucleophiles in which the nucleophilic atom is the same, nucleophilicities parallel basicities: RO HO RCO 2 ROH H2 O Nucleophiles parallel basicity when comparing atoms in the same period Nucleophiles do not parallel basicity and, instead, parallel size when comparing atoms of the same group The best leaving groups are weak bases after they depart Polar aprotic solvents favor SN 2and polar protic solvents favorSN 1Most of the solvents with abbreviated names are polar aprotic6.4 Elimination Reactions Higher temperatures increase the rates of elimination reactions A product with a more substituted double bond is more stable and thus more favorable Iftert-butoxideis used, sterics must be considered to nd out which hydrogen it takes through the6.5 Summary Note: It is debatable, but secondary molecules can haveSN 17orE1in polar protic solventsE2reaction
7Alkenes and Alkynes I - Overview7.1 The E-Z System To determineEorZ , look at the two groups attached to one carbon atom of the double bond.Decide which has higherpriority. Then, repeat this at the other carbon atom. If the two groups of higher priority are on the same side of the double bond, the alkene is designatedZ.If the two groups of higher priority are on opposite sides of the double bond, the alkene is designatedE.7.2 Relative Stabilities of Alkenes The trans isomer is generally more stable than the cis isomer The greater number of attached alkyl groups, the greater the stability of an alkene7.3 Factors A ecting Elimination Reactions A non-bulky base favors the more substituted double bond while a bulky base favors in making the less substituteddouble bond7.4 Acid-Catalyzed Dehydration of Alcohols Rearrangements, also known as 1,2 shifts, can occur in primary and secondary alcohol dehydration The more favored product is dictated by the stability of the alkene being formed For dehydration of secondary alcohols, the positive charge is shifted through a hydride shift or alkyl shift For the dehydration of primary alcohols, a carbocation is not formed as an intermediate. However, rearrangements canstill occur after dehydration. The resulting alkene'sπbond is broken when a hydrogen atom from the acid bonds tothe carbon to form a carbocation. Rearrangement then occurs as usual. A ring can change in size due to a methyl shift, especially to reduce ring strain. An example is shown below: Note: Never do two migrations8
Part IIIReaction Mechanisms8Ionic Reactions - Mechanisms8.1 The SN 2 Reaction Occurs with inversion of con guration If the bond to a chirality center is broken, there is an inversion of stereochemistry9
8.2 The SN 1 Reaction AnSN 1reaction will cause racemization if enantiomers are possible products8.3 The E2 Reaction There must be an anti-coplanar nature10
8.4 The E1 Reaction E1 reactions almost always accompany9SN 1reactions to some extentAlkenes and Alkynes I - Mechanisms9.1 Acid-Catalyzed Dehydration of Secondary or Tertiary Alcohols: An E1 Reaction11
9.2 Acid-Catalyzed Dehydration of Primary Alcohols: An E2 Reaction9.3 Synthesis of Alkynes from Vic-Dihalides Alkynes can be synthesized from alkanes via compounds called vicinal dihalides, which are compounds bearing thehalogens on adjacent carbons It requires the use ofNH 2,which can frequently be found asNaNH2withNH4 Cl9.4 Substitution of the Acetylenic Hydrogen Atom of a Terminal Alkyne A primary halide and a strong base must be used9.5 Deprotonation ReagentsThere are two good reactant choices:1.NaNH2and liquidNH32. LDA12
9.6 Hydrogenation Metal catalyzedH2addition to an alkyne (eg:H2 addition to anfor H2 /Ni2 B(P 2) Controlled metal catalyzedaddition (cis). This is alsoH2 /Pd-C)produces an alkanealkyne (eg:H25and Lindlar's Catalyst ) produces an alkene with syn- Chemical reduction of an alkyne produces an alkene with anti-addition (trans). Sodium metal and liquidexample. Another is10Li, C2 H5withNH4 ClAlkenes and Alkynes II - Mechanisms10.1 Addition of H X to an Alkene Markovnikov, not stereospeci c, and rearrangements are possible10.2 Acid-Catalyzed Hydration of an Alkene Markovnikov, not stereospeci c, and rearrangements are possible10.3 Mercuration-Demercuration and Hydroboration-Oxidation Mercuration-Demercuration: Markovnikov addition, anti stereochemistry, and no rearrangements UsesHg(OAc)2 , H2 Oand thenNaBH4 , NaOH Hydroboration-Oxidation: Anti-Markovnikov addition, syn stereochemistry, and no rearrangements Uses5 Lindlar'sBH3Catalyst isand thenH2 O2 , NaOHPd/CaCO3 /Pb13NH3is one
10.4 Summary of H X and H OH Additions10.5 Electrophilic Addition of Bromine and Chlorine to Alkenes14
10.6 Halohydrin Formation from an Alkene A halohydrin is produced when the halogenation of an alkene is carried out in an aqueous solution as opposed to anon-nucleophilic solvent If the alkene is unsymmetrical, there is anti-Markovnikov addition10.7 Oxidative Cleavage of Alkenes O3orKMnO4 Hot, basiccan perform oxidative cleavage of alkenes with syn additions (useful for adding multiple hydroxyl groups)KMnO4cleaves the double bond of an alkene.Disubstituted alkene carbons are oxidatively cleaved toketones, monosubstituted alkene carbons are cleaved to carboxylic acids, and unsubstituted alkene carbons are oxidizedto carbon dioxide. Using ozone - ozonolysis - is the best method to cleave alkenes and can open up cycloalkenes, as in the followingexample. The reagents are10.8OsO4O3 , CH2 Cl2and thenMe2 SReaction For details of this reaction, see the table below It is important to keep the backbone the same to ensure proper stereochemistry. An example is shown below:15
10.9 Summary for Dihalide, Dihydroxy, and Carbene Additions10.10Electrophilic Addition of Bromine and Chlorine to Alkynes Alkynes show the same kind of halo-addition as alkenes (anti-addition) Addition may occur once or twice depending upon the molar equivalents of the halogen reagent10.11Addition of Hydrogen Halides to Alkynes Alkynes react with one molar equivalent ofHXto form haloalkenes and with two molar equivalents to form geminaldihalides via Markovnikov's Rule Anti-Markovnikov addition occurs when peroxides are present10.12Oxidative Cleavage of Alkynes Oxidative cleavage of alkynes with ozone will yield two carboxylic acids11Alcohols and Ethers - Mechanisms11.1 Alcohols with H X Racemic mixtures are produced if enantiomers are possible Rearrangements are present Methanol and1 alcohols go through anSN 2mechanism.162 and3 alcohols go through anSN 1mechanism
11.2 Alcohols with PBr3 or SOCl2 Converts a1 or2 alcohol to a leaving group without rearrangements Inversion of con guration occurs since the reaction isSN 211.3 Leaving Group Derivatives of Alcohols Using either pyridine or DMAP, sulfonate esters can be prepared from combining an alcohol with a chlorinated sulfonatederivative There is retention of con guration with this reaction11.4 Converting OH to LG Summary11.5 Synthesis of Ethers Alcohols can dehydrate to form alkenes, as mentioned inSection 7.Also,1 alcohols can dehydrate to form ethers bythe following mechanism: Acid-catalyzed dehydration is not useful for preparing unsymmetrical ethers from di erentreaction leads to a mixture of products (ROR,0ROR ,and01 alcohols because the0R OR ) Alkoxymercuration-demercuration is a method for synthesizing ethers directly from alkenes, like in the example below,and parallels oxymercuration-demercuration17
11.6 Protecting Groups To add a protecting group to an alcohol, use TBD
1 Graphics are obtained mostly from Stony Brook University CHE 327 PowerPoint slides and Organic Chemistry , 10th Edition by Solomons and ryhle.F 3. Part II Organic Trends and Essentials 1 The Basics: Bonding and Molecular Structure 1.1 Resonance Stability File Size: 2MBPage Count: 20Explore furtherOrganic Reactions Summary For Use as a Study Guide Beauchampwww.cpp.eduOrganic Chemistry Reaction Summary Sheet DAT Bootcampdatbootcamp.comNAME REACTIONS AND REAGENTS IN ORGANIC SYNTHESISstromindia.weebly.comOverview of Types of Organic Reactions and Basic Concepts .profiles.uonbi.ac.keOrganic Chemistry I For Dummies Cheat Sheet - dummieswww.dummies.comRecommended to you b
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Types of Organic ReactionsTypes of Organic Reactions 1. Addition Reactions: A1. Addition Reactions: A B C HO OH O O H 2O HO OH O O OH fumarate malate 2. Elimination Reactions: D E F HO OH O O H 2 HO OH O O succinate fumarate 3. Substitution Reactions: G-H I G-I
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ii. acid–base neutralization reactions iii. oxidation–reduction or redox reactions. Q.3. What are the important aspects of redox reactions? Ans: Almost every element participate in redox reactions. The important aspects of redox reactions are as follows: i. Large number of natural, biological and industrial processes involve redox reactions .
Chemical Reactions Slide 3 / 142 Table of Contents: Chemical Reactions · Balancing Equations Click on the topic to go to that section · Types of Chemical Reactions · Oxidation-Reduction Reactions · Chemical Equations · Net Ionic Equations · Types of Oxidation-Reduction Reactions · Acid-Base Reactions · Precipitation Reactions
‘Tom Sawyer!’ said Aunt Polly. Then she laughed. ‘He always plays tricks on me,’ she said to herself. ‘I never learn.’ 8. 9 It was 1844. Tom was eleven years old. He lived in St Petersburg, Missouri. St Petersburg was a town on the Mississippi River, in North America. Tom’s parents were dead. He lived with his father’s sister, Aunt Polly. Tom was not clean and tidy. He did not .
