Chem Final Review Chapter Three

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Chem Final Review Chapter Three
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2013-12-06 14:59:18
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  1. A series of compounds that differ only by the number of -CH2- groups is called __ and the individual the series are called __
    • homologous series
    • homologs
  2. The __ is based on the number of carbons attached.
    degree of alkyl substitution
  3. Alkanes are nonpolar, so they dissolve in nonpolar or weakly polar organic solvents. Alkanes are said to be __ because they do not dissolve in water. 
    Because alkanes are __ than water and insoluble in water, a mix of an alkane looks like what?
    • hydrophobic 
    • less dense
    • it sparates into two phases with teh alkane on top
  4. Explain BP of alkanes
    • the BP increases sommothly with increasing numbers of carbon atoms and increaseing MW
    • - larger molecules have larger surface areas--> increased VdWattractions
  5. Explain MP of alkanes
    • MP increases with increasing MW
    • even numbers pack better so higher temps are needed to melt them
  6. Alanes can react with __ to form __. Heat or light is usually needed to initiate this __.
    • halogens
    • alkyl halides
    • halogenation
  7. Structure of methane
    ...ethane
    • tetrahedral with angles of 109.5
    • two methyl groups with sp3 hybrid orbitals forming a sigma bond around it
  8. Different arrangements formed by rotations around a single bond are called __, ad a specific conformation is called a __.
    • conformations
    • conformer
  9. In drawing conformations, we often use __, a way of drawing a molecule looking straight down the bond connecting two carbon atoms.
    Newman projections
  10. __ picture the molecule looking down at an angle toward the carbon-carbon bond. 

    Any conformation can be specified by its __, the angle between the C-H bonds on the front carbon atom and the C-H bonds on hte back carbon in the Newman projectin. Two of the conformations have special names. The conformation with angle of 0 is acalled __ because the Newman projection shows the hydrogen atoms on the back carbon to be hidden (__) by those on the front carbon. The __, with an angle of 60 degrees, has the hydrogen atoms on the back carbon staggered halfway between the hydrogens on the front carbon. Any other intermediate conformation is called __.
    sawhorse structures

    dihedral angle

    eclipsed conformation

    eclipsed

    staggered conformation

    skew conformation
  11. As ethane rotates towards an eclipsed conformation, its __ increases, and there is __ to the rotation. This resistance to twisting (__) is called __, and the energy required is called __.
    • potential energy
    • resistance
    • torsion
    • torsional strain
    • torsional energy
  12. There are three conformations. What are they?
    • totally eclipsed: when the methyl groups (in terms of butane)  θ= 0
    • the other eclipsed is at θ= 120 
    • at θ=60, the molecule is staggered and the methyl groups are toward the left and right of each other: this is gauche 
    • another staggered arrangement is θ= 180, with the methyl groups in opposite directions: called anti
  13. All the __ are lower in energy than any of the __. The __ is lowest in energy because it places the bulky methyl groups as far apart as possible. The __, with the methyl groups just 60 degrees apart, are higher in energy than the __.
    • staggered conformations
    • eclipsed conformaitons
    • anti
    • gauche 
    • anti
  14. Why is the totally eclipsed higher in energy than the regular eclipsed?
    because it forces the two end methyl groups so close together that their electron clouds experience a strong repulsion. This is called steric strain.
  15. The lowest energy conformation for any straight-chain alkane is the one with all the internal C-C bonds in their __.
    anti conformations
  16. The cycloalkanes are held in a more compact __, so their physical properties are similar to those of the __.
    • cyclic shape
    • compact, branched alkanes
  17. A cycloalkane has two distinct faces. If two substituents point towrad the same face, they are __; opposite= __.
    • cis 
    • trans
  18. If a cycloalkane requires bond angles other than 109.5, the orbitals of its C-C bonds cannot achieve optimum overlap, and the cycloalkane must have some __ (sometimes called __) associated with it.
    • angle strain
    • Baeyer strain
  19. In addition to angle strain, there is also strain from the eclipsing, which gives rise to __. Angle strain and __ give rise to __.
    • torsional strain x2
    • ring strain
  20. When is the extra energy released in a highly ring strained particle??
    combustion
  21. Cyclohexane forms what which places the groups 109.5 degrees apart. The __ also does this, but is different in the possition of its footrest methylene group, causing __ strain. This conformation has __ because they point upward from the ends of hte boat like two flagpoles.
    • a chair conformation
    • boat conf
    • torsional
    • flagpole hydrogens
  22. Substituents on a chair conformation should be __ for maximized stability.
    equatorial
  23. What is the steric strain attributed to?
    the 1,3- diaxial interaction, which involves substituents on carbon atoms of teh ring that bear a 1,3 relatoinship
  24. A larger group usually has a larger energy difference betweent he __ and __ because the __ is stronger for larger groups.
    • axial
    • equatorial
    • 1,3-diaxial interaction
  25. In general, if both groups cannot be equatorial, then what happens?
    the one with the larger group in an equatorial position is the most stable
  26. What are the three ways that two rings may be joined?
    • fused rings: sharing two adjacent carbon atoms and the bond between them
    • bridged rings: sharing two nonadjacent carbon atoms (bridgehead carbons) and one or more carbon atoms (the bridge) between them
    • spirocyclic compounds: two rigns share only one carbon atom

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