Orgo 16.1-16.5

Card Set Information

Author:
DesLee26
ID:
255141
Filename:
Orgo 16.1-16.5
Updated:
2014-01-05 20:56:44
Tags:
CHM 202
Folders:
Organic Chemistry
Description:
Price
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user DesLee26 on FreezingBlue Flashcards. What would you like to do?


  1. Benzenes are called __ because of their pleasant odors. Other organic compounds are called __, meaning "fatlike."

    A cyclic structure for benzenes with three double bonds (the cyclic structure with alternating single and double bonds) is called the __. However, it has its errors. What is it? 

    What was suggested?
    • aromatic
    • aliphatic
    • Kekule structure

    it predicts two different 1,2-dichlorobenzenes, but only one is known to exist

    a fast equilibrium interconverts the two isomers
  2. In a __ structure, the __ would be longer than the __. Spectroscopic methods have shown that the benzene ring is __ and all bonds are the same length. Because the ring is planar and the carbon nuclei are positioned at equal distances, the two __ structures must differ only in the positioning of the __.
    • Kekule structure
    • C-C single bonds
    • double bonds
    • planar
    • Kekule 
    • pi electrons
  3. __ is actually a resonance hybrid of the two __ structures. This representation implies that the __ are delocalized, with a bond order of 1.5 between adjacent carbon atoms. The carbon-carbon bond lengths in benzene are shorter than typical __, yet longer than typical double-bond lengths.
    • benzene
    • Kekule structures
    • pi electrons
    • single-bond lengths
  4. Benzene and its derivatives are __. Because the __ are delocalized over the ring, we use a circle to draw the double bonds to help remember what? 

    Benzene is a ring of six __ carbon atoms, each bonded to one hydrogen atom. All the carbon-carbon bonds are the same length, and all the bond angles are exactly 120 degrees. Each __ carbon atom has an unhybridized p orbital perpendicular to the plane of the ring, and six electrons occupy this circle of p orbitals.
    • benzenoid aromatic compounds
    • pi bonds
    • there are no localized single or double bonds and prevents us from trying to draw supposedly different isomers that differ only in the placement of double bonds in the ring


    • sp2 hybrid
    • sp2
  5. We can define an __ to be a cyclic compound containing some number of conjugated double bonds and having an unusually large resonance energy. 

    Benzene is actually much more __than we would expect from simple resonance-delocalized picture. Both the __ and the __ show that benzene is a __. Benzene's reactions are quite unusual.
    • aromatic compound
    • stable
    • Kekule structure
    • resonance-delocalized picture
    • cyclic conjugated triene.
  6. Addition of a catalyst such as ferric bromide to the mixture of bromine and benzene causes what to happen? __ is evolved as a byproduct, but the expected __ of __ does not take place. Instead, the organic product results from __ of a bromine atom for a hydrogen, and all three double bonds are retained.  
    • bromine color to disappear slowly
    • HBr gas
    • addition
    • Br2
    • substitution
  7. Benzene's reluctance to undergo typical alkene reactions suggests that it must be __. By comparing __, we can get a quantitative idea of its stability. __, __, and __ all hydrogenate to form cyclohexane. 

    The huge resonance energy of benzene cannot be explained by __ alone. The __ for benzene is actually smaller than that for __. The hydrogenation of the first double bond of benzene is __, the first endothermic hydrogenation we've encountered. In practice, this reaction is hard to stop after the addition of 1 mole of H2 because what? Clearly, the benzene ring is __.
    • unusually stable
    • molar heats of hydrogenation
    • benzene
    • cyclohexene
    • cyclohexadienes

    • conjugation effects
    • heat of hydrogenation
    • cyclohexa-1,3-diene
    • endothermic
    • exceptionally unreactive

    because the product hydrogenates more easily than benzene itself
  8. For years, chemists thought benzene's __ resultted from its two identical, stable resonance structures. They thought other jydrocarbons with __ of alternating single and double bonds would show similar stability. These cyclic hydrocarbons with alternating single and double bonds are called __.
    • large resonance energy 
    • analogous conjugated systems annulenes
  9. For the double bonds to be completely __, the __ must be __ so the p orbitals of hte pi bonds can overlap. As long as an __ is assumed to be planar, we can draw two __ that seem to show a benzene-like resonance. 

    __ has bever been isolated and purified. It undergoes an extremely fast __. To avoid the __, __ has been prepared at low concentrations in the gas phase and as individual molecules trapped in frozen argon at low temperatures. This is not hte behavior we expect from a molecule with exceptional stability.
    • conjugated
    • annulene
    • planar
    • annulene
    • Kekule-like structures
    • cyclobutadiene
    • Diels-Alder dimerization x2
    • cyclobutadiene
  10. IN 1911, Richard Willstaer synthesized __ and fond that it reacts like a normal __. Bromine adds readily to __, and __ oxidizes its double bonds. This evidence shows that __ is much less stable than benzene. in fact, structural studies have shown that __ is not __. It is most stable in a __ conformation, with poor overlap between adjacent pi bonds.
    • cyclooctatetraene
    • polyene
    • cyclooctatetraene
    • permanganate
    • cyclooctatetraene x2
    • planar
    • tub
  11. __ provides the key to understanding __ and predicting which compounds will have the stability of an aromatic system. 

    Benzene has a __ ring of six __ hybrid carbon atoms, each with an __ p orbital that overlaps with the p orbitals of its neighbors to form a continuous ring of orbitals above and below the plane of the carbon atoms. Six __ are contained in this ring of overlapping p orbitals.
    • molecular orbital theory
    • aromaticity
    • planar 
    • sp2 
    • unhybridized
    • pi
  12. The six overlapping p orbitals create a __. __ differ from __ and the __. A 2D __ requires 2D __, with the possibility of two distinct __ having the same energy. 

    What are the first two principles?
    • cyclic system of MOs x2
    • linear systems
    • allyl system
    • MOs

    • 1) There are six atomic p orbitals that overlap to form the benzene pi system. Therefore, there must be six molecular orbitals
    • 2) The lowest-energy molecular orbital is entirely bonding with constructive overlap between all pairs of adjacent p orbitals. There are no vertical nodes in this lowest-lying MO
  13. What are the last three principles?
    • 3) The number of nodes increases as the MOs increase in energy
    • 4) The MOs should be evenly divided between bonding and antibonding MOs, with the possibility of nonbonding MOs in some cases
    • 5) We expect that a stable system will have filled bonding MOs and empty antibonding MOs
  14. In a __, the intermediate energy levels are __ with two orbitals at each energy level. Both __ and __ have one nodal plane as we expect at the second energy level. Notice that __ has _ bonding interactions and __ antibonding ones, for a total of two net bonding interactions. Similarly __ has __ bonding interactions and __ nonbonding interactions, also totaling two net bonding interactions. Although we can't use the number of bonding and antibonding interactions as a quantitative measure of an orbital's energy, it is clear that __ and __ are bonding MOs, but not as strongly bonding as __.
    • cyclic system of overlapping p orbitals
    • degenerate (equal in energy)
    • π2 and π3
    • π2
    • four
    • two
    • π3
    • two 
    • four
    • π2 and π3
    • π1
  15. The next orbitals, __ and __ are also __, with __ in each. The __ has __ antibonding and __ nonbonding interactiosn; it is an __ orbital. Its __ partner, __, has __antibonding interactions and __ bonding interactions, for a total of two __ interactions. This degenerate pair of MOs, __ and __, are about as strongly antibonding as __ and __ bonding.
    • π4*
    • π5*
    • degenerate
    • two nodal planes
    • π4*
    • two
    • four
    • antiboding (*)
    • degenerate
    • π5*
    • four
    • two
    • antibonding
    • π4*
    • π5*
    • π2
    • π3
  16. The __ has __ nodal planes. Each pair of adjacent p orbitals is __ and interacts __.

    The __ for benzene shows three pi bonds, representing six electrons involved in __ bonding. Six electrons fill the three bonding __ of the __. This electronic configuration explains the unusual stability of benzene. The first MO is __ and is particularly stable. The second and third (__) MOs are still strongly bonding and all three of these bonding MOs __ the electrons over several nuclei. This configuration, with all the bonding MOs filled, is energetically very favorable.
    • π6*
    • three
    • out of phase
    • destructively

    • Kekule structure
    • pi
    • MOs
    • benzene system
    • all-bonding
    • degenerate
    • delocalize
  17. __ is unstable. Its instability is explained by the molecular orbitals. Four __ hybrid carbon atoms form the __ ring, and their four p orbitals overlap to form four __.The lowest energy MO is __, the __ with no nodes.

    The next two orbitals, __ and __, are __, eaech having one __ nodal plane. Each of these MOs has __ bonding interactions and __ antibonding interactions. The net bonding order is __, so these two MOs are __. The final MO, __, has two __ and is entirely __.
    • cyclobutadiene
    • sp2
    • cyclobutadiene
    • MOs
    • π1
    • all-bonding MO

    • π2 and π3
    • degenerate (equal energy)
    • symmetrically situated
    • two x2
    • zero
    • nonbonding
    • π4*
    • nodal planes
    • antibonding
  18. The localized structure of cyclobutadiene shows two __, implying four __. Two electrons fill π1, the __. Once π1 is filled, two orbitals of equal energy are avalable for the remaining two electrons. If the two electrons go into the same orbital, they must have paired spins and they must share the same region of space. Since electrons __ each other, less energy is required for the electrons to occupy different __, with __. This principle is another application of __.
    • double bonds
    • pi electrons
    • lowest-lying orbital
    • repel
    • degenerate orbitals
    • unpaired spins
    • Hund's rule
  19. Cyclobutadiene should be __. Its highest-lying electrons are in __ and are therefore very __. According to __, the compound exists as a __ in its ground state. Such a __ is expected to be extremely reactive. Thus, __ successfully predicts the dramatic stability difference between benzene and cyclobutadiene.
    • unstable
    • nonbonding orbitals
    • reactive
    • Hund's rule
    • diradical (two unpaired electrons) x2
    • MO theory
  20. The patterns of MOs in benzene and cyclobutadiene are similar to the patterns in other __: THe __ is the unique one with no nodes; thereafter, the MOs occur in __ until only one highest-lying MO remains. In benzene, the energy diagram looks like the hexago of a benzene ring. In cyclobutadiene, the pattern looks like the diamond of the cyclobutadiene ring.
    • annulenes
    • lowest-lying MO
    • degenerate (equal-energy) pairs
  21. The __ states tha tthe MO energy diagram of a regular, completely conjugated cyclic system has the same __ shape as the compound, with one __ (the all-bonding MO) at the bottom. The nonbonding line cuts __through the center of the __.
    • polygon rule
    • polygonal
    • vertex 
    • horizontally
    • polygon
  22. Aromatic compounds are those that meet the following criteria: 
    1 and 2
    • 1) The structure must be cyclic, containing some number of conjugated pi bonds
    • 2) Each atom in the ring must have an unhybridized p orbital (The ring atoms are usually sp2 hybridized or occasionally sp hybridized)
  23. Aromatic compounds are those that meet the following criteria: 
    3 and 4
    • 3) The unhybridized p orbitals must overlap to form a continuous ring of parallel orbitals. In most cases, the structure must be planar (or nearly planar) for effective overlap to occur
    • 4) Delocalization of the pi electrons over the ring must lower the electronic energy
  24. An __ is one htat meets the first three criteria, but delocalization of hte pi electrons over the ring increases the electronic energy. Aromatic structures are more stable than their __ counterparts. 

    Cyclobutadiene meets the first three criteria for a continuous ring of overlapping p orbitals, but __ of the pi electrons does what?

    Cyclobutadiene is less stable than its __, and it is __.
    • antiaromatic compound
    • open-chain counterparts
    • delocalization
    • increases the electronic energy
    • open-chain counterpart
    • antiaromatic
  25. A cyclic compound that does not have a continuous, overlapping ring of p orbitals cannot be __ or __. It is said to be __, or __. It's electronic energy is similar to that of its __.
    • aromatic
    • antiaromatic
    • nonaromatic
    • aliphatic
    • open-chain counterpart

What would you like to do?

Home > Flashcards > Print Preview