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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
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
naming alkyl halides
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)
many alkyl halides that are widely used have common names
Many Alkyl Halides That Are Widely Used Have Common Names
  • Chloroform
  • Carbon tetrachloride
  • Methylene chloride
  • Methyl iodide
  • Trichloroethylene
alcohols
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
naming alcohols
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),
iupac rules for naming alcohols
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
many alcohols have common names
Many Alcohols Have Common Names
  • These are accepted by IUPAC
properties of alcohols hydrogen bonding
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
acids and bases the br n sted lowry definition
Acids and BasesThe Brønsted-Lowry Definition
  • Acid – A proton (H+) donor
  • Base – A proton acceptor

Acid Base Conjugate Conjugate

Acid Base

predicting acid base reactions from p k a values
Predicting Acid – Base Reactions from pKa 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

lewis acids and bases
Lewis Acids and 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
kinds of organic reactions
Kinds of Organic Reactions
  • 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
how organic reactions occur mechanisms
How Organic Reactions Occur: Mechanisms
  • 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
steps in mechanisms
Steps in Mechanisms
  • 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
types of steps in reaction mechanisms
Types of Steps in Reaction Mechanisms
  • 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
breaking of covalent bonds
Breaking of Covalent Bonds

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
formation of a bond
Formation of a Bond

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
indicating steps in mechanisms
Indicating Steps in Mechanisms
  • 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’)
5 6 using curved arrows in polar reaction mechanisms
5.6 Using Curved Arrows in Polar Reaction Mechanisms
  • 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
5 4 polar reactions and how they occur
5.4 Polar Reactions and How They Occur
  • 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
electronegativity of some common elements
Electronegativity of Some Common Elements
  • The relative electronegativity is indicated
  • Higher numbers indicate greater electronegativity
  • Carbon bonded to a more electronegative element has a partial positive charge (+)
polarizability
Polarizability
  • 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
generalized polar reactions
Generalized Polar Reactions
  • 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
10 7 preparing alkyl halides from alcohols
10.7 Preparing Alkyl Halides from Alcohols
  • 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
5 10 describing a reaction intermediates
5.10 Describing a Reaction: Intermediates
  • 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