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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
- homologs
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The __ is based on the number of carbons attached.
degree of alkyl substitution
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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
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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
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Explain MP of alkanes
- MP increases with increasing MW
- even numbers pack better so higher temps are needed to melt them
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Alanes can react with __ to form __. Heat or light is usually needed to initiate this __.
- halogens
- alkyl halides
- halogenation
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Structure of methane
...ethane
- tetrahedral with angles of 109.5
- two methyl groups with sp3 hybrid orbitals forming a sigma bond around it
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Different arrangements formed by rotations around a single bond are called __, ad a specific conformation is called a __.
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In drawing conformations, we often use __, a way of drawing a molecule looking straight down the bond connecting two carbon atoms.
Newman projections
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__ 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
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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
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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
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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
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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.
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The lowest energy conformation for any straight-chain alkane is the one with all the internal C-C bonds in their __.
anti conformations
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The cycloalkanes are held in a more compact __, so their physical properties are similar to those of the __.
- cyclic shape
- compact, branched alkanes
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A cycloalkane has two distinct faces. If two substituents point towrad the same face, they are __; opposite= __.
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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
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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
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When is the extra energy released in a highly ring strained particle??
combustion
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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
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Substituents on a chair conformation should be __ for maximized stability.
equatorial
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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
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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
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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
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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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