Organic Chemistry ACS Final IV – Flashcards
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species with an unpaired electron, electron deficient, highly reactive, no formal charge
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free radicals
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do we need to use a solvent when working with radicals? why or why not?
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no, because they are electrically neutral
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What are the two general types of free-radical reactions in organic chemistry?
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1. substitution 2. addition
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What are the two free radical addition reactions discussed in undergraduate organic chemistry?
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1. addition of HBr to alkenes in the presence of peroxides 2. polymerazation of alkenes to dienes
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What is a great way to tell if something is a free radical addition reaction?
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The reactions are initiated by heat, peroxides, or UV light
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All radical reactions are chain reactions that proceed through three general steps. What are the three steps?
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1. Initiation 2. Propagation 3. Termination
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Generates radicals
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initiation
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involves a radical reacting with a stable molecule to produce a new radical
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propagation
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destroys radical and stops the reaction
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termination
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Reflects the relative stability of a radical
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the energy required for the generation of organic radicals
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They require the least energy to form and are generated most rapidly
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the most stable radical
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The stability of radicals generally increases with
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increasing substitution on the carbon atom that carries the unpaired electron
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easy to generate because they are stabilized through resonance
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allylic and benzylic radicals
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what is the general trend for stability of organic radicals
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allylic benzylic > 3 alkyl > 2 alkyl > 1 alkyl > methyl > vinylic/aryl
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A reaction usually involves radicals if any of these reactants or conditions are present
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AIBN (a radical initiator) peroxides (RO-OR) UV light (indicated by hv) high temperature (300-500 Celsius)
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When an achiral radical reacts with something, the attack can happen on either face, because of these we see ____________ in the product
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racemization
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Of primary, secondary, tertiary, which hydrogen atom is most easily abstracted by free radical halogenation
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the tertiary hydrogen
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the position next to a benzene ring
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the benzylic position
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the free radical bromination of alkylbenzenes leads to substitution at the ___________ position
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benzylic
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The reactions of alkenes with HBr in the presence of peroxides are free-radical addition reactions that proceed through
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intermediate carbon radicals CH-CH*-CHBr
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A reaction in which a radical reacts with an alkene or diene to produce a new, larger radical
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free radical polymerization
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What happens in the polymerization of 1,3-dienes?
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-dbl bonds are formed between C-1 of one monomer and C-4 of another monomer -the two double bonds become single bonds in the process and a double bond forms between C-2 and C-3
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increasing the oxygen content and/or decreasing the hydrogen content of a compound
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oxidation
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decreasing the oxygen content and/or increasing the hydrogen content of a compound
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reduction
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The most widely used oxidizing agents are
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chromium reagents and manganese reagent CrO3 K2Cr2O7 K2CrO4 KMnO4
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the chromium reagents are normally used under
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acidic conditions
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the potassium permanganate is normally used under
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basic conditions
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potent oxidizers that usually do not stop until all of the hydrogen atoms attached to the carbon atoms undergoing oxidation have been romoved
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chromic acid hot, basic permanganate
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what reagent is used to oxidize primary alcohols which stops at the aldehyde stage
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CrO2 PCC PDC
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react with alkenes, alkynes, and alkylbenzenes to give oxidative cleavage products
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hot chromic acid hot basic permanganate
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when oxidizing alkylbenzenes, where does the oxidation occur
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at the benzylic carbon atom to produce benzoic acid
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cleavage of vicinal diols is done by
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periodic acid (HIO4)
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cleavage of alkenes is done by
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ozone
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cleavage of methyl ketones is done by
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alkaline solutions of the halogens (haloform reaction
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react with alkenes and alkynes to give oxidative addition products
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cold, alkaline permanganate osmium tetroxided peroxy acids
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usually performed with complex metal hydrides
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reductions of carbonyl compounds
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reductions of alkenes are performed with
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catalytic hydrogenation
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reductions of alkynes are performed with
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catalytic hydrogenation alkali metals in ammonia
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what special reactions are available for reduction of the C=O groups of aldehydes and ketones all the way to CH2 groups
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Clemmenson reduction Wolff-Kischner reduction desulfuration of thiol acetals/ketals by Raney nickel
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converts primary alcohols to carboxylic acids and secondary alcohols to ketones
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chromic acid (K2Cr2O7/H2SO4)
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converts primary alcohols to aldehydes and secondary alcohols to ketones BUT does not affect C=C bonds or C-C triple bonds
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PCC
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conversion of a methyl ketone to a carboxylic acid is done by
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haloform reaction using I2/KOH
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after reductive workup, cleavage of alkenes with ozone results in the formation of
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aldehydes and ketone
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cleavage of an acyclic alkene results in the formation of
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two molecules
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cleavage of a cyclic alkene gives an
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acyclic product
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a convenient way to remember how ozone cleaves double bonds
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imagine stretching the C=C bond and mentally replacing the C=C with C=O and O=C
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cleaves the C-C bond of alpha-hydroxy aldehydes and ketones, alpha dicarbonyl compounds, and 1,2-diols in which the OH groups can achieve a cisoid conformation.
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reactivity of diols with periodic acid
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when a diol reacts with periodic acid(HIO4), the mechanism of cleavage involves a five member intermediate, and this intermediate cannot be made with
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TRANS-1,2-diol
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The only diols cleaved by periodic acid (HIO4) are
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1,2-diols
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The product of the cleavage of a 1,2-diol by periodic acid (HIO4) has to have what type of hydroxyl groups
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cis
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what reagent can be used to reduce a triple bond to a double bond having Z (cis) geometry? (reduction of alkynes to alkenes)
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BaSO4 stops at the alkene stage
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Types of catalysts that are used to produce Z alkenes from alkynes
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Pd with some deactivating agent. Usually: Pd/BaSO4 Pd/BaCO3 Lindlars catalyst Poisoned Pd deactivated Pd
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Will reduce a ketone to an alcohol but will also reduce the alkene group
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H2/Pd
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reduces ketones to secondary alcohols but will not react with alkenes or esters
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NaBH4
