3 -- Part 2: STRUCTURE AND STEREOCHEMISTRY OF ALKANES
Droplets can't burn as efficiently as a Vapor, so the engine would smoke and give low mileage.
Heptane and isooctane were once added to be prone to knocking.
A variable gasoline is used in a test engine to increase the octane rating compression ratio.
The compression and lubricate the valves are caused by higher compression ratios.
The ratio is increased until knocking begins.
The percent lead was banned from automotive age of isooctane in isooctane/heptane blend that begins to knock at any given gasoline because it inactivates the catalytic compression ratio.
The octane number assigned to the gasoline is simply the percent converters and introduces lead into the age of isooctane in an isooctane/heptane mixture that begins to knock at that same environment.
TEL is used in a compression ratio.
There are higher-boiling liquids that are somewhat viscous.
Significant quantities of volatile diesel fuel are used in the production of these alkanes.
Kerosene has been used.
The heavier fuel in vocs is allowed to burn by the use of lamps and heaters.
Jet fuel is more refined and less odorous than long-chained alkanes.
The components of air pollution top of the compression stroke are sprayed directly into the cylinder of a diesel engine.
The hot, highly compressed air in the cylinder causes and contributes to cardiac and the fuel to burn quickly.
Diesel fuel becomes a semisolid mass after partial solidification.
Diesel engine owners in cold climates mix a small amount of gasoline with their diesel fuel in the winter.
The slush can be pumped to the cylinders with the added gasoline.
lubri cating and heating oils are often used with more than 16 carbon atoms.
Mineral oils come from petroleum, which used to be considered a mineral.
Alkanes Paraffin "wax" is not a true wax, but a mixture of high-molecular-weight alkanes with melting points well above room temperature.
Chapter 25 talks about the true waxes.
The majority of alkanes are derived from by-products.
Alkanes, aromatics, and some undesirable compounds are the principal components of crude oil.
A refinery must be adjusted to process a particular type of crude oil, as the composition of petroleum and the amount of contaminants vary from one source to another.
Light Arabian crude, West Texas crude, and other classes of crude petroleum are paid different prices because of their different qualities.
A careful fractional distillation is the first step in refining.
The mixture of alkanes with useful ranges of boiling points is not pure alkanes.
The table shows the major fractions.
The process of Catalytic Cracking involves heating alkanes in the presence of materials that break large molecule into smaller ones.
Cracking can be used to make higher-boiling fractions into gasoline blends.
The following reaction shows the hydrocracking of a molecule.
CH3 2 or Al2O3 catalysts can be used to separate petroleum into fractions.
Natural gas is pumped and stored all over the world.
Depending on the source of the gas, natural gas is 70% methane, 10% ethane, and 15% propane.
There are also small amounts of other hydrocarbons.
Natural gas can be found above pockets of petroleum or coal, but also in places where there is little or no coal.
Natural gas is used to heat buildings and generate electricity.
It's important as a starting material for the production of fertilizers.
The methane we burn as natural gas is millions of years old, but another 300 million tons of new methane is created by microbes in diverse places such as the stomachs of plant-eating animals and the mud under the sea.
Most of the methane is eaten by other organisms.
Methane escapes when it is brought to the surface.
There are no practical methods for capturing and using naturally occurring methane or methane hydrate.
Methane is a greenhouse gas that contributes to global warming.
The least reactive class of organic compounds is alkanes.
Alkanes do not react with strong acids or bases.
The most useful reactions of alkanes take place under conditions.
The rate of the reaction is difficult to control and the conditions are inconvenient in a laboratory.
Alkane reactions are formed under high amounts of products that are difficult to separate.
There is pressure on the cold seafloor.
When important for an industry, the products quickly melt rated and sold separately.
The methane may eventually be released by newer methods of functionalization.
The following alkane reactions are used in the chemical industry, but they are rarely seen in laboratory applications.
The burning of gasoline and fuel oil depletes the resources needed for lubricants and chemical feedstocks.
Solar and nuclear heat sources do not deplete natural resources.
The more environment-friendly heat sources are more expensive than the ones that use alkanes.
The maximum yields of gasoline are what the cracking process usually operates under.
Alkanes can form alkyl halides.
methane reacts with chlorine to form chloromethane, dichloro methane, methylene chloride, and trichloromethane.
Reactions with fluorine are often too fast to control.
Iodine doesn't react very quickly or at all.
Chapter 4 will discuss the halogenation of alkanes.
Alkanes have many of the same structural characteristics as other organic compounds.
The central carbon atom has four hydrogen atoms bonding to it.
Three sigma orbitals forming a bond.
The sigma bond connecting the two carbon atoms is not fixed in a single position, but is free to rotate.
As carbon atoms turn, the bond maintains its linear bonding overlap.
In most cases, pure conformers can't be isolated because they are constantly rotating.
The front carbon atom has three lines coming together in a Y shape.
The back carbon is represented by a circle.
If you don't know Newman projections, you should make models and compare them with the drawings.
The angle between the hydrogen atoms on the front and back carbons can take on an infinite number of values.
The IUPAC definition requires that a conformer correspond to a potential energy minimum, such as the anti and gauche conformations of butane.
Skew is a term used to describe any other conformation.
From the direction of the blue arrows, draw Newman projections of the following molecules.
From the direction of the arrow, the front carbon has a group pointing straight up, a chlorine group pointing to the left, and a hydrogen group pointing to the right.
The back carbon has an ethyl group pointing straight down, a bromine pointing up and to the left, and a hydrogen pointing up and to the right.
Depending on how the eye sees them, sawhorse structures can be misleading.
We will usually use Newman projections.
Two of the conformations have special names.
In a sample of ethane gas at room temperature, the ethane molecule rotates at a rate of millions per second.
Some of the conformations are favored more than others.
H bonds were separated as much as possible.
The energy of the staggered conformation is lower than that of the eclipsed one because of the interactions of the electrons in the bonds.
A small amount of energy is not enough to overcome a small rotational barrier.
As the carbon- carbon bond rotates, the potential energy of ethane changes.
ethane's potential energy increases and there is resistance to the rotation.
Many reactions depend on a molecule's ability to twist into a particular conformation, and it is possible to predict which conformations are favored and which reactions are more likely to take place.
We will apply analysis to propane and butane first.
The C bond of propane has the same energy as ethane, but with a different amount of energy.
The carbon-carbon bonds were overshadowed by the H bond.
The graph shows the torsional energy of propane as one of the carbon-carbon bonds rotates.
The third of ethane's torsional energy is that of the eclipsed conformation.
The strain from eclipsing a carbon-hydrogen contributes 5.4 kJ/mol.
The chain of carbon atoms is not straight.
The angles between the carbon atoms are very close.
The center bond in butane has different shapes.
Three of them have names.
There is a chance of rotation about any of the carbon-carbon bonds.
They do it in ethane and propane.
C3 bonds are more interesting.
The dihedral angle is the angle between the two end groups.
The groups eclipse each other when they are pointed in the same direction.
The butane molecule is staggered and the methyl groups are to the left and right of each other.
The methyl groups point in opposite directions when there is another staggered conformation.
There is a graph of the butane's relative torsional energies.
The staggered conformations are lower in energy than the eclipsed ones.
The bulky methyl groups are placed far apart by the anti conformation.
The gauche's energy is 3.8 kJ higher than the anti's because the methyl groups are close enough that their electron clouds begin to repel each other.
You can use your models to compare the crowding of the groups.
The totally eclipsed conformation has a higher energy than the other ones because it forces the two end methyl groups so close together that their electron clouds experience a strong repulsion.
The totally eclipsed conformation is the highest in energy.
The interference between the groups is shown in the structure.
Most, but not all, of the steric strain can be released by rotating the completely eclipsed conformation.
The gauche is 3.8 kJ higher in energy than the most stable anti conformation.
We can apply what we have learned about butane to other alkanes.
There is enough thermal energy in the room to allow the molecule to move quickly among all the different energy.
The term "steric hindrance" refers to the slowing of a reaction because bulky groups interfere.