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
strong acids or bases
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
__ is a rapid oxidation that takes place at high temps, converting __ to __.
Little control over the reaction is possible, except for __ and __.
controlling the fuel/ air ratio to achieve efficient burning
Burning of gas and fuel oil causes __.
Catalytic __ of large hydrocarbons at high temps produces __.
The cracking process usually operates under conditions taht give the max yields of gasoline
In __, hydrogen is added to give __; cracking without hydrogen gives mixtures of __ and __.
Alkanes can react with __ to form __.
Heat or light is usually needed to initiate this __. Reactions of alkanes with __ and __ proceed at moderate rates and are easily controlled.
The simplest alkane: __
two-carbon alkane is composed of two methyl groups with overlapping sp3 hybrid orbitals forming a sigma bond between them
In ethane, the two methyl groups are not __ but are relatively __ about the __ connecting the __.
fixed in a single position
free to rotate
two carbon atoms
The bond maintains its __ as the carbon atoms turn.
linear bonding overlap
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.
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 __.
three lines coming together in a Y shape
a circle with three bonds pointing out from it
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
__ picture the molecule looking dwn at an angle toward the C-C bond.
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 __.
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.
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 __
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.
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.
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.
Three kC is not a large amount of energy
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 __.
__ 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
__ is the three carbon alkane, with formula C3H8.
__ is the four-carbon alkane (C4H10)
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.
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.
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 __.
Another staggered conformation occurs at At θ= 180 degrees, with the __ pointing in opposite directions. This conformation is called __ because the __ groups are __.
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)
The __, with the methyl groups separated by just sixty degrees, are 3.8 kJ higher in energy than the __. Why?
the methyl groups are close enough that their electron clouds begin to repel each other.
The __ is about 6 kJ higher in energy than the other __ because it does what?
totally eclipsed conformation
it forces the two end methyl groups so close together that their electrons clouds experience a strong repulsion
tHIS KIND OF INTERACTION between two bulky groups is called __.
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
We can predict that C-C single bonds will assume __ whenever possible to avoid __ attached to them.
eclipsing of hte groups
Among the __, the __ is preferred because it has the __.
lowest torsional energy
The relative stabilities are important because what?
more molecules will be found in the more stable conformations than in the less stable ones