Chem Final Review Chapter Three
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A series of compounds that differ only by the number of -CH2- groups is called __ and the individual the series are called __
- homologous series
The __ is based on the number of carbons attached.
degree of alkyl substitution
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?
- less dense
- it sparates into two phases with teh alkane on top
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
Explain MP of alkanes
- MP increases with increasing MW
- even numbers pack better so higher temps are needed to melt them
Alanes can react with __ to form __. Heat or light is usually needed to initiate this __.
- alkyl halides
Structure of methane
- tetrahedral with angles of 109.5
- two methyl groups with sp3 hybrid orbitals forming a sigma bond around it
Different arrangements formed by rotations around a single bond are called __, ad a specific conformation is called a __.
In drawing conformations, we often use __, a way of drawing a molecule looking straight down the bond connecting two carbon atoms.
__ 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 __.
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
- torsional strain
- torsional energy
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
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
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.
The lowest energy conformation for any straight-chain alkane is the one with all the internal C-C bonds in their __.
The cycloalkanes are held in a more compact __, so their physical properties are similar to those of the __.
- cyclic shape
- compact, branched alkanes
A cycloalkane has two distinct faces. If two substituents point towrad the same face, they are __; opposite= __.
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
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
When is the extra energy released in a highly ring strained particle??
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
- flagpole hydrogens
Substituents on a chair conformation should be __ for maximized stability.
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
A larger group usually has a larger energy difference betweent he __ and __ because the __ is stronger for larger groups.
- 1,3-diaxial interaction
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
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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