ch. 5 - alcohols and alkyl halides: introduction to...

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CH. 5 - ALCOHOLS AND ALKYL HALIDES: INTRODUCTION TO REACTION MECHANISMS (PART.1)

CONCEPT: FUNCTIONAL GROUPS

● We can group several millions of different molecules into subsets of similar _________________________

1. Hydrocarbons

● All carbon groups regardless of size can be symbolized using an _______ group.

● When an alkane is attached to a greater carbon chain, it is given an ________ suffix. (i.e. __________ group)

● Carbons are given a “degree” based on how many other ____________ they are attached to

□ Hydrogens possess the __________ degree as the carbon they are attached to

□ Degrees are expressed as primary, secondary, tertiary and quaternary (1⁰, 2⁰, 3⁰, 4⁰)

EXAMPLE: Determine the degree of the indicated carbons and hydrogens

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2. Alkyl Halide _________

● Any –R group directly attached to a halogen.

● The degree of alkyl halide is determined the same way as __________________

The carbonyl ____________ is NOT a functional group, but it is a major component of many functional groups

3. Alcohol ____________ 6. Carboxylic Acid ______________(_________) ● Degree of alcohol is determined the same ● The acid of organic chemistry way as ____

4. Amine ______________ 7. Amide _______________(___________)

Degree of alcohol is determined the same ● Degree of alcohol is determined the same way as ____. way as ____.

5. Ether __________________ 8. Ester __________________(___________)

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9. Carbonyls

The term “ carbonyl” is not the proper name of the functional groups because the functionality of the group depends on its location on the carbon chain.

.

● Ketone ______________(__________) ● Aldehyde ______________(__________)

- _______________carbonyl group - _______________carbonyl group

10. Nitrile ________________

11. Benzene

● Directly attached to –R group _______________ (_________)(_____)

● Extra CH2 between –R group _______________ (_____________)(_____)

EXAMPLE: Identify all the functional groups in the following compound. Show degrees where applicable.

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12. Other Carbonyl Compounds

● Acyl Chloride (__________) ● Anhydride (_______________)

13. Sulfur Compounds

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PRACTICE: Identify all the functional groups in the following compound. Show degrees where applicable.

a.

b.

c.

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CONCEPT: ALKYL HALIDES

Alkyl halides are named by naming them as a substituent before the root chain and indicating their location.

● Prefixes: -F ______________, -Cl _______________ -Br ________________ -I ______________

Alkyl halides have NO ________________ when it comes to numbering the direction of the chain.

EXAMPLE: Name the following compounds:

a.

b.

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CONCEPT: ALCOHOL NOMENCLATURE

□ Alcohols are named by adding the modifier (-_______) the end of the root.

● Alcohols receive _______________ priority in numbering alkanes

● Locations can be donated _______________ the root “old school” or _______________ the root “new school”

EXAMPLE: Name the following compound:

a.

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CONCEPT: THE HAMMOND-POSTULATE

□ The Hammond-Postulate more accurately describes what transition states look like. Paraphrased version:

● Transition state that resembles reagents = ____________ ● Transition state that resembles products = ___________

EXAMPLE: Determine which species has higher energy in the following reactions. Identify the transition state as early or

late, and correctly draw it.

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CONCEPT: CARBOCATION INTERMEDIATES — STABILITY

□ Carbocations are stabilized by a phenomenon called _________________________________

● Hyperconjugation is the delocalization of charge by the interaction of an empty p-orbital with an adjacent, eclipsed σ-bond

● Since this is only possible with -R groups, the more substituted the carbocation, the more ________________

EXAMPLE: Which of the following alkyl halides would generate the most stable carbocation?

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CONCEPT: CARBOCATION INTERMEDIATES — REARRANGEMENTS

□ Carbocations will rearrange to an adjacent, more stable position if possible. This is called a ___________

● 1,2-Hydride Shift occurs when there is a ____________ located on an adjacent, more stable carbon.

● 1,2-Alkyl Shift occurs when only small __________ groups are located on an adjacent, more stable carbon.

● Ring Expansion occurs when a carbocation is adjacent to a 3, 4 or 5- membered ring.

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PRACTICE: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

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CONCEPT: INTRODUCTION TO SUBSTITUTION

Previously, we discussed the various ways that acids could react with bases:

□ Recall that in these mechanisms, electrons always travel from ________ density to _______ density

Bronsted-Lowry Reactions: When a nucleophile and electrophile react to exchange a ______________

Lewis Acid/Base Reactions: When a nucleophile and electrophile with an empty orbital react to form a covalent bond

Substitution Reactions take place when a nucleophile reacts with an electrophile that does not have an empty orbital.

□ This generates the need to analyze a new type of conjugate base: the leaving group.

EXAMPLE: Predict the product. Identify all of the chemical species in the following reaction.

● In typical acid and base reactions, we used stability of the conjugate base to determine chemical equilibrium

● In substitution, we use the stability of the leaving group to help determine reaction rate.

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CONCEPT: LEAVING GROUPS

Leaving groups break a bond with the electrophile to make it reactive. They are molecules that will remain stable after

accepting an extra electron pair.

□ We use factors affecting acidity to determine which atoms will be most stable after gaining extra electrons.

● Recall that the element effect consists of two trends:

EXAMPLE: Predict which of the following pairs of electrophiles possesses the best leaving group

a. b.

c. d.

□ Due to their high electronegativity, __________ ______________ will be the primary leaving groups for this chapter.

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CONCEPT: THE SN2 MECHANISM

□ A negatively charged nucleophile reacts with an accessible leaving group to produce substitution in one-step.

SN2 Properties (Circle One)

● Nucleophile = Strong / Weak

● Leaving Group = Unsubstituted / Highly Substituted

● Reaction coordinate = Transition State / Intermediate

● Reaction = Concerted / Two-Step

● Rate = Unimolecular / Bimolecular

● Rate = k[RX] / k[Nu][RX]

● Stereochemistry = Inversion / Retention / Racemic

● Nickname = ______________________________________

EXAMPLE: Rank the following alkyl halides in order of reactivity toward an SN2 reaction.

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PRACTICE: Provide the mechanism and final products for the following reactions.

a.

b.

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CONCEPT: THE SN1 MECHANISM

□ A neutral nucleophile reacts with an inaccessible leaving group to produce substitution in two-steps.

The more -R groups, the more substituted the carbocation, the more ________________

SN1 Properties (Circle One)

● Nucleophile = Strong / Weak

● Leaving Group = Unsubstituted / Highly Substituted

● Reaction coordinate = Transition State / Intermediate

● Reaction = Concerted / Two-Step

● Rate = Unimolecular / Bimolecular

● Rate = k[RX] / k[Nu][RX]

● Stereochemistry = Inversion / Retention / Racemic

● Nickname = ______________________________________

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PRACTICE: Provide the mechanism and final products for the following reactions.

□ NOTE: Substitution reactions with neutral nucleophiles require an additional deprotonation step.

a.

b.

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CONCEPT: SUBSTITUTION COMPARISON

When given a substitution reaction, use the following two factors to determine the mechanism:

1. Nucleophile Strength SN1 = ___________ SN2 = ___________

2. Leaving Group Substitution SN1 = ___________ SN2 = ___________

EXAMPLE: Provide the mechanism and final products for the following reactions.

a.

b.

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CONCEPT: CONVERSION OF ALCOHOLS TO GOOD LEAVING GROUPS

□ Alcohols are terrible leaving groups. If we want to react with them, they need to be transformed.

●They can be converted into ____________ _________________ or ______________ _______________

2o and 3o Alcohols with HX: SN1 mechanism

1o alcohols with HX: SN2 mechanism

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□ SOCl2 and PBr3 are two of the most commonly used reagents to transform alcohols into alkyl halides

●They always proceed with __________________________ of configuration.

1o and 2o Alcohols to RX: SN2 mechanism

EXAMPLE: Determine the mechanism for the following reaction. Draw the final product.

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□ Alcohols can attack sulfonyl chlorides to create sulfonate esters.

●They always proceed with __________________________ of configuration.

Alcohols to Sulfonate Esters:

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Alcohol Conversion Summary:

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ch. 5 - alcohols and alkyl halides: introduction to...

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