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85 Cards in this Set
- Front
- Back
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what constitutes the double bond in an alkene? |
one sigma and one pi bond
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what is the hybridization of the carbons in the c=c double bond of alkenes?
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sp2 |
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what is the bond angle in alkenes?
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120 degrees
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what is the geometry of alkenes?
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trigonal planar
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what are the three types of alkenes?
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terminal, internal and cycloalkenes.
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why do alkenes undergo many reactions that alkanes do not??
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because alkenes contain pi bonds which are much weaker and more easily broken that the sigma bonds in alkanes.
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what kind of forces do most alkenes exhibit?
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weak VDW
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do alkenes generally have low or high boiling points
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low
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how are melting points and boiling points affected by number of carbons?
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the more carbons, the higher the mp and bp due to increase in surface area
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what are alkenes soluble in ?
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organic solvents - they are insoluble in water!
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what is the rule for assigning priorities?
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the higher the atomic number, the higher the priority!
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a _____ (cis or trans) alkene is more polar than a ____ (cis or trans) alkene, giving it a slightly higher boiling point and making it more soluble in polar solvents
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a cis alkene is more polar than a trans alkene, giving it a slightly higher boiling point and making it more soluble in polar solvents
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what bonds do alcohols, ethers and epoxides all have in common?
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c-o sigma bonds
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what hybridization and geometry do all the 'O' atoms have in alcohols, ethers and epoxides?
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tetrahedral and sp3 hybridized
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what are the bond angles in ethers and epoxides?
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109.5
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what is the bond angle in an epoxide?
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60 degrees
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what kind of strain do epoxides have?
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angle strain!
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how do you number along the carbon chain when naming alcohols?
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to give OH the lowest possible number!
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where does the numbering always start when naming cyclic alcohols?
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at the OH (always at the c1 position)
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what are compounds with two hydroxy (OH) groups called?
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diols
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what are compounds with three hydroxy groups called?
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triols
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what suffix do alcohols get?
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-ol
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how are simple ethers named?
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1) look at either side of the 'O' in the ether and name the two alkyl groups separately
2) put in alphabetical order 3) add the word "ether" to end |
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how are more complex ethers named?
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you can name the more simple group of the two (group+O) as an ALKOXY substituent, changing the -yl ending to -oxy, then name the more complicated part as an alkane.
(methOXY) (ethOXY) (tert-butOXY) etc., etc, |
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what's one way to name epoxides?
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as an epoxyalkane (easiest) just name the alkane chain or ring and use the prefix "epoxy" to the name oxygen as a substituent. use TWO numbers to designate the O's location
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what are the three ways to name epoxides?
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as epoxyalkanes, oxiranes, or alkene oxides
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what are the two rules for ordering boiling points?
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1)hydrogen bonding increases bp,
2)bp increases as the extent of hydrogen bonding increases (with alcohols, hydrogen bonding increases and thus bp increases 3<2<1) 1* is the highest bp, 3* is the lowest bp |
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of alcohols, ethers and epoxides, which is capable of intermolecular hydrogen bonding?
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alcohols
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what decreases the extent to which alcohols are capable of hydrogen bonding?
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more r-groups! more r-groups, less effecient hydrogen bonding
so 3* alcohols are least capable of h-bonding! |
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how are alcohols, ethers and epoxides prepared?
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Sn2 reactions of alkyl halides with strong nucleophile
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what is the preparation of ethers via sn2 reaction called ?
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williamson ether synthesis
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if there is more than one possible route to form an ether, which is the preferred path?
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the less hindered one (less r-groups)
the less r-groups, better route to form ether via willaimson method |
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when do epoxides form?
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when a compound contains both a hydroxy group and a halogen atom on adjacent carbon atoms.
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what occurs during dehydration of an alcohol?
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the elements of OH and H are lost off of alpha and beta carbons (respectively) via beta elimination reaction!!
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what is dehydration typically carried out using?
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H2SO4 (and other strong acids!)
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what is the order of increasing rate of dehydration of alcohols?
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more substituted alcohols dehydrate faster! (3* first, 1* last) remember, 1* alcohols have highest boiling point) and dehydrate slowest
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during dehydration of an alcohol, if two or more stereoisomers are possible, which will be the major product?
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the more substituted one
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what is introduced when an alcohol is dehydrated?
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since the reaction is beta elimination a double bond should be in the product!
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if ranking alcohols in order of reactivity when dehydrated with H2So4, in what order would they fall?
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the rate of dehydration increases as the number of r groups increases (3* alcohol would react quickest, 1* would react slowest)
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for 2* and 3* alcohols, what type elimination do they undergo during dehydration?
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E1
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what type of elimination do 1* alcohols undergo in dehydration?
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E2
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what is always needed in an elimination reaction (dehydration of alcohols)?
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a strong base to protonate the O atom to form a good leaving group
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what's a carbocation rearrangement?
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when a less stable carbocation rearranges to become more stable (more r groups!)
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what are carbocation rearrangements called?
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1,2-shift
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in carbocation rearrangments, what is the movement of a hydrogen called?
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1,2-halide shift
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in carbocation rearrangements, what is the movement of a methyl group called?
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1-2, alkyl shift (ex: 1,2 methyl shift) movement of a methyl
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when can carbo cation rearrangement occur?
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whenever carbocations are formed as intermediates (ANY SN1 or E1 reaction)
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when POCl3 is used in dehydration instead of a strong acid, what mechanism takes place?
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E2
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for an alcohol to undergo substitution reaction what must the starting material be treated with?
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HX (because OH needs to be converted to a good leaving group) so SN never occurs when alcohol is treated with just X (halide)
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what is produced when alcohol reacts with HX?
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1*, 2* and 3* alkyl halides.
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more substituted alcohols react faster or slower with HX?
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faster (3* alcohol is fastest)
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what are the 2 mechanisms for reaction of an alcohol with HX?
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SN2 and Sn1
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what type of reaction do methyl and 1* alcohols undergo with HX?
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Sn2
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what type of reactions do 2* and 3* alcohols undergo with HX?
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Sn1
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when methyl or 1* alcohols react with HX they undergo SN2...what stereochemistry occurs?
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inversion of configuration
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when 2* and 3* alcohols react with HX they undergo Sn1...what stereochemistry occurs?
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racemization
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tosylates are generally treated with strong bases and nucelophiles, as a result most of the reactions they undergo are what?
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SN2 and E2
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tosylates + strong nucleophile =
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Sn2 reaction! inversion of configuration
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tosylates + strong base =
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E2 (dont forget addition of double bond)
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what are the only 2 strong acids that can react with ethers to form a good leaving group?
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only HBR and HI
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what happens when ethers react with HBr or HI?
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both C-O bonds are cleaved and 2 alkyl halides are formed as products
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by what means does ether cleavage occur?
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sn2 or sn1
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in an unsymmetrical epoxide, where does the nucleophile attack when reaction is with STRONG (negatively charged) NUCLEIOPHILE?
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at the less substituted carbon atom
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what usually occurs during the reaction of epoxides?
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a strong nucleophile is used- SN2 occurs
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in an unsymetrical epoxide, where does the nucleophile attack when reaction is with HZ?? (Hbr, ect.)
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at the more substituted carbon atom
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what types of forces do alkenes exhibit usually?
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only vdw forces
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how do you determine 'r' or 's' and 'e' and 'z'
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by looking at the atom BONDED directly, and considering it's atomic number! higher the atomic number, higher the priority
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what kind of reactions do alkenes and alkynes undergo?
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addition!
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why do alkenes and alkynes undergo addition reactions?
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because they have an easily broken pi bond (alkynes have 2)
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what is always in the product of an elimination reaction?
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a double bond!
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what always happens in addition reactions? what is added, taken away in products and reactants?
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a double bond is broken, and TWO new sigma bonds are formed
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how are alkenes prepared?
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elimination reactions!!!! with [alkyl halide + strong base] or [alcohol + strong acid]
for example: dehydrohalogenation (elimination) via reaction of alkyl halide with strong base (E2 reaction) |
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electrophillic addition consists of two successive _________ reactions
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lewis acid-base
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what rule does addition to alkenes follow?
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markovnikovs rule! which means that during the addition of HX to alkenes, the H-atom bonds to the LESS substituted carbon atom
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what is markovnikov's rule?
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in addition reactions to alkene during the addition of HX, the h-atom bonds to the LESS substituted carbon atom
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what does regioselective mean?
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a regioselective reaction is one that yeilds a particular constitutional isomer that predominates when more than one is actually possible
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what KIND of electrophillic addition occurs with the addition of HX (hydrohalogenation) to an alkene?
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syn AND anti
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alcohols add to alkenes to form what?
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ethers
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what is formed during halogenation?
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halogenation is (x2) and VICINAL dihalides are formed !
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what two addition reactions form carbocations as intermediates?
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hydrohalogenation and hydration
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what 2 addition reactions form bridged halonium ions as intermediates?
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halogenation and halohydrin formation
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what addition reaction occurs in one step?
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hydroboration-oxidation
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br2 and h20 form what from alkenes?
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bromohydrins
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what does hydroboration oxidate ultimately result in?
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the syn addition of OH and H
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when are "alkylboranes" formed and what are they?
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in hydroboration-oxidation reactions. aklylboranes are the middle product formed with just 1 equivilent of alkene.
(when the H and BH3 are added, before the OH replaces BH3) |
