Orgo Ch 3.6-3.8

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Orgo Ch 3.6-3.8
2013-09-25 23:14:42
CHM 201

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  1. Alkanes are the __ class of organic compouds. Their low reactivity is reflected in another term for alkanes: __. 

    Chemists found that alkanes do not react with __ or __ or with most other __. They attributed this __ to a lack of __ for other reagents--> named them paraffins
    • least reactive
    • paraffins
    • strong acids or bases
    • reagents
    • low reactivity
    • affinitiy
  2. Most useful reactions of alkanes take place under __. Alkane reactions often form mixtures of products that are difficult to separate. 
    These mixtures may be commercially important where the products may be separated and sold separately.
    energitic or high temperature conditions
  3. __ is a rapid oxidation that takes place at high temps, converting __ to __.

    Little control over the reaction is possible, except for __ and __.
    • combustion
    • alkanes
    • CO2
    • water
    • moderating temperature
    • controlling the fuel/ air ratio to achieve efficient burning
  4. Burning of gas and fuel oil causes __.
    air polution
  5. Catalytic __ of large hydrocarbons at high temps produces __.
    The cracking process usually operates under conditions taht give the max yields of gasoline
    • cracking
    • smaller hydrocarbons
  6. In __, hydrogen is added to give __; cracking without hydrogen gives mixtures of __ and __.
    • hydrocracking
    • saturated hydrocarbons
    • alkanes
    • alkenes
  7. Alkanes can react with __ to form __.
    • halogens
    • alkyl halides
  8. Heat or light is usually needed to initiate this __. Reactions of alkanes with __ and __ proceed at moderate rates and are easily controlled.
    • halogenation
    • chlorine
    • bromine
  9. The simplest alkane: __
    Explain it
    • methane
    • tetrahedral (109,5)
    • sp2
  10. Explain ethane
    two-carbon alkane is composed of two methyl groups with overlapping sp3 hybrid orbitals forming a sigma bond between them
  11. In ethane, the two methyl groups are not __ but are relatively __ about the __ connecting the __.
    • methyl groups
    • fixed in a single position
    • free to rotate
    • sigma bond
    • two carbon atoms
  12. The bond maintains its __ as the carbon atoms turn.
    linear bonding overlap
  13. The different arrangements formed by rotation about a single bond are called __, and a specific conformation is called a __. Pure __ cannot be isolated in most cases, because the molecules are constantly rotation through all the possible conformations.
    • conformations
    • conformer
    • conformers
  14. In drawing conformations, we often use __, a way of drawing a molecule looking straight down the bond connecting two carbon atoms.
    The front carbon atom is represented by __.
    The back carbon is represented by __.
    • Newman projections
    • three lines coming together in a Y shape
    • a circle with three bonds pointing out from it
  15. Why is an infinite number of conformations possible for ethane?
    because the angle between the H atoms on the front and back carbons can take on an infinite number of values
  16. __ picture the molecule looking dwn at an angle toward the C-C bond.
    Sawhorse structures
  17. Any conformationc an be specified by its __, the angle between the C-H bonds on the front carbon atom and the C-H bonds on the back carbon in the __.
    • dihedral angle
    • Newman projection
  18. Two of the conformations have special names. The conformation with θ= 60o , is called the __ because the Newman projection shows the hydrogen atoms on the back carbon to be hidden (__) by those on the front carbon.
    • eclipsed conformatoin
    • eclipsed
  19. The __, with  θ= 60o, has the hydrogen atoms on the back carbon staggered halfway between the hydrogens on the front carbon. Any other intermediate conformation is called a __
    • staggered conformation
    • skew conformation
  20. True or False:
    In an sample of ethane gas at room temp, the ethane molecules rotate millions of times per second, and their conformations are constantly changing. These conformations are not all equally favored, however.
  21. The lowest- energy conformaiton is __, with the electron clouds in the C-H bonds separated as much as possible. The interactions of the electrons in the bonds make the __ about 12.6 kJ/mol higher in energy than the __ conformatin.
    • staggered conformation
    • eclipsed conformation
    • staggered conformation
  22. True or False:
    Three kilocalories is a large amount of energy, and at room temp, most molecules have enough kinetic energy to overcome this small rotational barrier.
    • False:
    • Three kC is not a large amount of energy
  23. As ethane rotates toward an eclipsed conformation, its potential energy increases, adn there is __ to the rotation. This __ to twisting (__) is called __, and the 12.6 kJ/mol of energy required is called __.
    • resistance x2
    • torsion
    • torsional strain
    • torsional energy
  24. __ is the study of the energetics of different conformations. Many reactions depend on a molecule's ability to twist into a particular conformation; __ can help to predict which conformations are favored and which reactions are more likely to take place.
    conformational analysis x2
  25. __ is the three carbon alkane, with formula C3H8.
  26. __ is the four-carbon alkane (C4H10)
  27. We refer to __ as a straight-chain alkane, but the chain of carbon atoms is not really straight. The angles between the carbon atoms are close to the __, about __. 
    Rotations about any of the __ are possible. 
    Rotations about either of the end bonds just rotate a __ like in ethane or propane.
    • n-butane
    • tetrahedral angle
    • 109.5
    • carbon-carbon bonds
    • methyl group
  28. When the __ are pointed in the same direction ( θ= 0 degrees), they eclipse each other. This conformation is called __, to distinguish it from the other eclipsed conformations like the one at  θ= 120 degrees.
    • methyl groups
    • totally eclipsed
  29. At  θ= 60 degrees, the __ molecule is staggered and the __ are toward the left and right of each other. This 60 degree conformation is called __.
  30. Another staggered conformation occurs at At  θ= 180 degrees, with the __ pointing in opposite directions. This conformation is called __ because the __ groups are __.
    • methyl groups
    • anti
    • methyl 
    • "opposed"
  31. All the __ are lower in energy than any of the __. The __ is lowest in energy because it places the bulky __ as far apart as possible.
    • staggered conformations (anti and gauche)
    • eclipsed conformations 
    • methyl groups
  32. The __, with the methyl groups separated by just sixty degrees, are 3.8 kJ higher in energy than the __. Why?
    • gauche conformations
    • anti conformation
    • methyl groups
    • the methyl groups are close enough that their electron clouds begin to repel each other.
  33. The __ is about 6 kJ higher in energy than the other __ because it does what?
    • totally eclipsed conformation
    • eclipsed conformations
    • it forces the two end methyl groups so close together that their electrons clouds experience a strong repulsion
  34. tHIS KIND OF INTERACTION between two bulky groups is called __.
    steric strain
  35. Rotating the __ sixty degrees to a __ releases most, but not all, of this steric strain. 
    The __ is still 3.8 kJ higher in energy than the most stable __>
    • totally eclipsed conformation
    • gauche conformation
    • gauche conformation
    • anti conormation
  36. We can predict that C-C single bonds will assume __ whenever possible to avoid __ attached to them.
    • staggered conformations
    • eclipsing of hte groups
  37. Among the __, the __ is preferred because it has the __.
    • staggered conformations
    • anti conformation
    • lowest torsional energy
  38. The relative stabilities are important because what?
    more molecules will be found in the more stable conformations than in the less stable ones

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