Unformatted text preview:

Chem 2520 Final Study Guide !!Chapter 15: Benzene and Aromaticity!!Aromaticity!-Huckel's Rule: electron count of a cyclic, conjugated system (planar) must fit the formula 4n + 2 (n=0, 1, 2...) to be aromatic !-4n are aromatic (unstable) !-Systems that do not apply are called nonaromatic!!Examples: !!!!!!!!!!!!!!!!!!Electrophilic Aromatic Substitution (EAS) !-Benzene is stable, electron rich, and nucleophilic !!!!!!-aromaticity is destroyed, then restored !!!Halogenation !-a catalyst is needed because halogens are weak electrophiles !!!!!!-mechanism !!!!!!!!!!!-chlorinations are possible (Cl2, FeCl3), but F2 and I2 are not !!Nitration !-The electrophile is a nitronium ion !!!!!!-mechanism !!!!!!!!!!!Sulfonation !-The electrophile is sulfur trioxide (SO3) !-fuming H2SO4 (about 8% SO3) !!-mechanism !!!!!!-sulfonation is reversible!!!!!!!!!!Friedel-Craft Alkylation !-The electrophile is a metallated alkyl halide !!!!-mechanism !!!!!!!Example: !!!!!!-this reaction can create undesired products from polyalkylations and rearrangements !-the rearrangements occur because the reaction goes through a carbocation, therefore carbocation rearrangements may occur!!!!!!-propyl carbocation can rearrange to be more stable via a hydride shift !!!!-in order to obtain products through the less stable carbocations Friedel-Crafts acylations are useful !!Friedel-Crafts Acylation !-more useful than alkylations and deactivate the ring!!!!!!!-AlCl3 is no longer a catalyst, but it is needed to pull the Cl off the acyl halide to form the acylium ion (the electrophile) !-H2O is a work up step !!-The electrophile is an acylium ion !!!!!!!!!!-mechanism !!!!!!-aqueous work up is required !!!!!!-can use carboxylate anhydrides !!!!!!-can remove the oxygen by the Clemmensen Reduction !!!!!!Chapter 16: Substituted Benzene Inductive Effects!-Donators/Activators donate electron density!-Acceptors/Deactivators withdraw electron density! !!!!!!!!!Resonance Effects!-will (almost) always trump induction!-donors/activators are functional groups with a lone pair directly on the ring!!!!!!!-Acceptors/deactivators contain polarized pi bonds directly on the ring !!!!!!!!Ortho/Para Directors!-all activators and weak deactivators (halogens) are o/p directors !!!!!!!!!-Strong activators have a lone pair next to the ring !-strong activation through resonance, weak deactivation through induction !!!!!!!!-Moderate activators have a lone pair next to the ring that is also tied up in resonance outside of the ring !!!!!!!-Weak activators are alkyl groups !-they have no resonance and are weak activators through induction !!!!!!!-Weak deactivators are halogens !-they are deactivating through induction and very weakly activating through resonance!-this is the exception to the rule! !!Why are activators o/p directors and not meta directors?!-all has to do with resonance stabilization !!!!!!!!!!!!-putting the electrophile at the o/p positions is the most stable as the second resonance structure has all octets. The meta position is not the most stable because it does not benefit from stabilization of the -OMe!!Why are halogens o/p directors when they are weak deactivators?!!!!!!!!!!!!-the explanation is the same as above in that the second o/p resonance structure is stable because it contains all octets. !! Meta Directors !-moderate/strong deactivators are meta directors!!!!!!!!-Strong deactivators have a pi bond to an electronegative atom next to the ring!-they are deactivating through resonance and induction !!!!!!!!!!-Moderate/strong deactivators are very powerfully electron withdrawing !-they have no resonance, but have a strong induction effect!!!!!!!Why are strong/moderate deactivators meta directors? !!!!!!!!!!!!!-when the electrophile is o/p to the deactivating group the structure is destabilized due to the inductive effect of CF3. When the electrophile is meta to the group the structure is not stabilized and for this reason it is a meta director. !!Predicting Directing Effects !Two rules:!1. Ortho/para directors always beat meta directors!2. The strongest activator wins!!-also, the effects are additive and sterics will dictate similar positions !!Examples: !!!!!!!!!!!!!Changing Directing Nature !!!!!!!!!!!!!!!!!!!Aniline and Phenol are Superactivated !-meaning they result in multiple additions !!!!!!!!!!Reducing the Activity of Functional Groups !-some FGs can be protected to reduce activity !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!EAS Reactions on Benzenoid Structures !-Napthalene will add at C1!!!!!!Why C1? !-attack at C1 will maximize aromatic resonance structures !-C1 generates 5 total resonance structures with 2 being aromatic!-C2 generates 5 total resonance structures with 1 being aromatic !!-activating substituents effect the ring that they are attached to!-o/p rules apply!!!!!!!-Deactivating substituents will add C5 and C8!-C5 and C8 are "C1" positions on other ring !!!!!!!!-Larger benzenoid reaction sites are determined based on resonance structures !!!**Three main functional groups that will render a ring too deactivated to do a Friedel-Craft's:!!!!!!!!!!!Chapter 17: Aldehydes and Ketones Oxidation of Alcohols!-Chromium Reagents!!!!!!!!!!!!!!!!-Manganese Reagents!-selective allylic -OH oxidation !!!!!!!Ozonolysis!!!!!!-the reductive work up makes it an aldehyde!!!!!Hydration of Alkynes!-Markovnikov!!!!!!-Anti-Markovnikov!!!!!!!Multiple Sites of Reactivity !!!!!!!!!!!-obey a general mechanism !!!!!!!!!!!!!Nucleophilic Addition-Protonation Mechanism (basic) !!!!!!!!Electrophilic Protonation-Addition (acidic) !!!!!!!!Neutral!!!!!!!!!Addition of Water - Hydrate Formation !-mechanism - (base-catalyzed) (aqueous -OH: H2O/NaOH) !!!!!!-H+ cat. mechanism (H3O+: H2O/HCl)!!!!!!-Reversibility!1. Alkyl groups stabilize carbonyls!2. Aldehydes are more electropositive and add faster than ketones !!!!!!!Addition of Alcohols - Hemiacetals and Acetals!!!!!!!-mechanism !!!!!!!!!!!!!Acetals as Protecting Groups !!!!!!!!!Thioacetals !!!!!!!-hydrolysis!!!!!!!!!!!!!Addition of Amines and Ammonia!-Formation of Imines: condensation reaction with a primary amine (orNH3)!!!!!!-mechanism (acidic)!!!!!!!!!!!-Imine Derivatives!!!!!!!!!!!!-Formation of Enamines: reaction with a secondary amine!!!!!!!-mechanism !!!!!!!Wolf-Kishner Reduction !!!!!!-mechanism!!!!!!Cyanohydrins!-addition of -CN to carbonyl!!!!!!The Wittig Reaction!-Addition of a phosphonium ylide to a carbonyl !!!!!!!!-mechanism!-ylide formation !!!!!!!!!-alkene formation


View Full Document
Download Final Study Guide
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Final Study Guide and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Final Study Guide 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?