Orgo 6.18-6.20

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  1. many compounds can eliminate in more than one way, to give __. 
    In most E1 and E2 eliminations where there are two or more possible elimination products, the product will be what?

    This general principle is called __ and reactions that give the most usbstituted alkene are said to follow __.
    mixtures of alkenes

    • will be the one with the msot substituted double bonds
    • Zaitsev's rule
    • Zaitsev orientation
  2. Zaitsev's rule
    in elim reactions, teh most subst. alkene usually predominates
  3. True or False:
    Eliminatiosn can also take place under second order conditions with a strong base present.

    The rate of the elimination is proportional to the concentrations of both the __ and the __, giving a __. This is a __ process, with both the base and the alkyl halide participating in the __, so this mechanism is abbreviated __ for __.
    • True
    • alkyl halide
    • base
    • second order rate equation
    • bimolecular
    • TS
    • E2
    • elimination, bimolecular
  4. Most strong nucleophiles are also strong bases, and elimination commonly results when a strong base/ nucleophile is used witha __ such as a tertiary or hindered secondary alkyl halide. instead of attacking the baci side of hte hindered __, for example, methoxide abstracts a proton from one of hte methyl groups. ONE STEP
    • poor Sn2 substrate
    • electrophilic carbon
  5. In the general mechanism of hte E2 reaction, a strong base abstracts a proton on a carbon atom adjacent to the one with the __. As the base abstracts a proton, a __ form s adn the the leaving group leaves. Like the Sn2 reaction, the E2 is a __ reaction in which bonds break and new bonds form at the same time, in a single step.
    • leaving group
    • double bond
    • concerted
  6. The order of reactivity of alkyl halides towards E2 dehydrohalogenation is found to be __.

    This reactivity order reflects the greater stablilty of __. Elimination of a tertiary halide gives a more __ than elim of a secondary halide, which gives a more __ than a primary. 

    The stabilities of the alkene products are reflected in the __, giving __ and __ that lead to highly substituted alkenes.
    • teritary > secondary> primary
    • substituted alkene x2
    • Tses
    • lower Ea
    • higher rates for elimination of alkyl halides
  7. The E2 reation requires abstraction of a proton a carbon atom __. If tehre are two or more possibilities, __ may result. In most cases, __ predicts which of the possible products will be the major product: __
    • next to the carbon bearing hte halogen
    • mixtures of products
    • Zaitsev's rule
    • most subs. alkene
  8. Key mechanism of E2
    signle step: strong base abstracts a proton on a carbon next tot he leaving group, and the leaving group leaves--> alkene
  9. Like the Sn2 reaction, the E2 follows a __: bond breaking and bond formation take place simultaneousyl, adn the partial formaiton of new bonds does what?.
    • concerted mechanism
    • lowers the energy of the transiton
  10. __ require specific geometric arrangements so tha tthe orbitals of the bonds being broken can __with those being formed and hte electrons can flow smoothly from one bond to another.

    The geometric arrangemnet required by Sn2 is a __; with teh E2, a __ is needed.
    • concerted mechanisms
    • overlap
    • backside attack
    • coplanar arrangement of the orbitals
  11. E2 elim requires partial formation of a new __, with its parallel p orbitals in the TS. The electrons that once formed a C-H bond must begin to __ with the orbital the the __ is vacating. Formation of this new __ implies that these two sp3 orbitals must be __ so that pi overlap is possible as the H and halogen leave and hte orbitals rehybridize to the p orbitals of hte new pi bond.
    • pi bond
    • overlap
    • leaving group
    • pi bond
    • parallel
  12. When th hydrogen and the halogen are __ to each other, their orbitals are aligned.
    This is called the __ conformation. When teh hydrogen and hte halogen __each other, their orbitals are once again aligned. This is called the __ conformation.
    • anti
    • anti-coplanr
    • eclipse
    • syn-coplanar
  13. Of these possible conformations, the __ is most commonly seen in E2 reactions. The transition state for __ is staggered, with the base far away from the leaving group. In most cases, this transition state is __ than that of the __.
    • anticoplanar
    • the anti coplanar
    • lower in energy
    • syn-coplanar elimination
  14. The transition stae for __ is an eclipsed conformation. In addition to the higher energy resulting from eclipsign interactions, the transition state suffers from __ between the __ and the __. To abstract the proton, the base must approach quite close to the __. In most cases, the __ is bulky and - charged, and the repulsion between the base and the leaving group raises the energy of the __.
    • syn-coplanar elimination
    • interference
    • leaving grop adn the attacking base
    • leaving group x2
    • syn coplanar TS
  15. Some molecuels are rigidly held in __ with a H and a leaving group in a __> Such compounds are likely to udnergo __ by a __.
    • eclipsed (or nearly) conformations
    • syn-coplanar arrangement
    • E2 elimination
    • concerted syn-coplanar mechanism
  16. The E2 is a __ reaction, because different stereoisomers of the starting material react to give different __ of the product. This __results from the  __ that is usually involved int eh E2.
    • stereospecific
    • stereospecificity 
    • anti-coplanar transition state

Card Set Information

Orgo 6.18-6.20
2013-10-30 10:53:50
CHM 201

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