Alcohol and alkyl halides
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Alcohol and Alkyl Halides. Chapter 3 . Alkyl Halides. An organic compound containing at least one carbon-halogen bond (C-X) X (F, Cl, Br, I) replaces H Can contain many C-X bonds Properties and some uses Fire-resistant solvents Refrigerants Pharmaceuticals and precursors.

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Alkyl halides l.jpg
Alkyl Halides

  • An organic compound containing at least one carbon-halogen bond (C-X)

    • X (F, Cl, Br, I) replaces H

  • Can contain many C-X bonds

  • Properties and some uses

    • Fire-resistant solvents

    • Refrigerants

    • Pharmaceuticals and precursors


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Naming Alkyl Halides

  • Name is based on longest carbon chain

    • (Contains double or triple bond if present)

    • Number from end nearest any substituent (alkyl or halogen)


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Many Alkyl Halides That Are Widely Used Have Common Names

  • Chloroform

  • Carbon tetrachloride

  • Methylene chloride

  • Methyl iodide

  • Trichloroethylene


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Alcohols

  • Alcohols contain an OH group connected to a a saturated C (sp3)

  • They are important solvents and synthesis intermediates

  • Phenols contain an OH group connected to a carbon in a benzene ring

  • Methanol, CH3OH, called methyl alcohol, is a common solvent, a fuel additive, produced in large quantities

  • Ethanol, CH3CH2OH, called ethyl alcohol, is a solvent, fuel, beverage

  • Phenol, C6H5OH (“phenyl alcohol”) has diverse uses - it gives its name to the general class of compounds


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Naming Alcohols

  • General classifications of alcohols based on substitution on C to which OH is attached

  • Methyl (C has 3 H’s), Primary (1°) (C has two H’s, one R), secondary (2°) (C has one H, two R’s), tertiary (3°) (C has no H, 3 R’s),


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IUPAC Rules for Naming Alcohols

  • Select the longest carbon chain containing the hydroxyl group, and derive the parent name by replacing the -e ending of the corresponding alkane with -ol

  • Number the chain from the end nearer the hydroxyl group

  • Number substituents according to position on chain, listing the substituents in alphabetical order


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Many Alcohols Have Common Names

  • These are accepted by IUPAC



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Properties of Alcohols: Hydrogen Bonding

  • The structure around O of the alcohol or phenol is similar to that in water, sp3 hybridized

  • Alcohols and phenolshave much higher boiling points than similar alkanes and alkyl halides



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Acids and BasesThe Brønsted-Lowry Definition

  • Acid – A proton (H+) donor

  • Base – A proton acceptor

Acid Base Conjugate Conjugate

Acid Base




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Predicting Acid – Base Reactions from p BasesKa Values

The proton will always go from the stronger acid to the stronger base

Acetic Acid Hydroxide Ion Acetate Ion Water

pKa = 4.76 pKa = 15.74



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Lewis Acids and Bases Bases

  • Lewis Acid – electron-pair acceptor

  • Lewis Base – electron-pair donor

  • Lewis Acids usually have at least one empty orbital

  • Lewis Bases usually have at least one set of paired electrons




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Kinds of Organic Reactions Bases

  • In general, we look at what occurs and try to learn how it happens

  • Common patterns describe the changes

    • Addition reactions – two molecules combine

    • Elimination reactions – one molecule splits into two

    • Substitution – parts from two molecules exchange

    • Rearrangement reactions – a molecule undergoes changes in the way its atoms are connected


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How Organic Reactions Occur: Mechanisms Bases

  • In a clock the hands move but the mechanism behind the face is what causes the movement

  • In an organic reaction, we see the transformation that has occurred. The mechanism describes the steps behind the changes that we can observe

  • Reactions occur in defined steps that lead from reactant to product


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Steps in Mechanisms Bases

  • We classify the types of steps in a sequence

  • A step involves either the formation or breaking of a covalent bond

  • Steps can occur in individually or in combination with other steps

  • When several steps occur at the same time they are said to be concerted


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Types of Steps in Reaction Mechanisms Bases

  • Formation of a covalent bond

    • Homogenic or heterogenic

  • Breaking of a covalent bond

    • Homogenic or heterogenic

  • Oxidation of a functional group

  • Reduction of a functional group


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Breaking of Covalent Bonds Bases

Homolytic Cleavage

  • Each product gets one electron from the bond

  • Not common in organic chemistry

    Heterolytic Cleavage

  • Both electrons from the bond that is broken become associated with one resulting fragment

  • A common pattern in reaction mechanisms


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Formation of a Bond Bases

Homogenic

  • One electron comes from each fragment

  • No electronic charges are involved

  • Not common in organic chemistry

    Heterogenic

  • One fragment supplies two electrons

  • One fragment supplies no electrons

  • Combination can involve electronic charges

  • Common in organic chemistry


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Indicating Steps in Mechanisms Bases

  • Curved arrows indicate breaking and forming of bonds

  • Arrowheads with a “half” head (“fish-hook”) indicate homolytic and homogenic steps (called ‘radical processes’)

  • Arrowheads with a complete head indicate heterolytic and heterogenic steps (called ‘polar processes’)


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5.6 Using Curved Arrows in Polar Reaction Mechanisms Bases

  • Curved arrows are a way to keep track of changes in bonding in polar reaction

  • The arrows track “electron movement”

  • Electrons always move in pairs

  • Charges change during the reaction

  • One curved arrow corresponds to one step in a reaction mechanism


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5.4 Polar Reactions and How They Occur Bases

  • Molecules can contain local unsymmetrical electron distributions due to differences in electronegativities

  • This causes a partial negative charge on an atom and a compensating partial positive charge on an adjacent atom

  • The more electronegative atom has the greater electron density


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Electronegativity of Some Common Elements Bases

  • The relative electronegativity is indicated

  • Higher numbers indicate greater electronegativity

  • Carbon bonded to a more electronegative element has a partial positive charge (+)


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Polarizability Bases

  • Polarization is a change in electron distribution as a response to change in electronic nature of the surroundings

  • Polarizability is the tendency to undergo polarization

  • Polar reactions occur between regions of high electron density and regions of low electron density


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Generalized Polar Reactions Bases

  • An electrophile, an electron-poor species, combines with a nucleophile, an electron-rich species

  • An electrophile is a Lewis acid

  • A nucleophile is a Lewis base

  • The combination is indicate with a curved arrow from nucleophile to electrophile


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10.7 Preparing Alkyl Halides from Alcohols Bases

  • Reaction of tertiary C-OH with HX is fast and effective

    • Add HCl or HBr gas into ether solution of tertiary alcohol

  • Primary and secondary alcohols react very slowly and often rearrange, so alternative methods are used


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5.10 Describing a Reaction: Intermediates Bases

  • If a reaction occurs in more than one step, it must involve species that are neither the reactant nor the final product

  • These are called reaction intermediates or simply “intermediates”

  • Each step has its own free energy of activation

  • The complete diagram for the reaction shows the free energy changes associated with an intermediate


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