In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond. The simplest alkenes, with only one double bond, no rings, and no other functional groups, are hydrocarbons with the general formula CnH2n.
Alkanes, also called paraffins, are a class of hydrocarbons that are fully saturated with hydrogen. They contain no double or triple bonds in their carbon skeletons and, therefore, have the maximum number of carbon to hydrogen covalent bonds.
The following is a list of the first 16 alkenes:
- Ethene (C2H4)
- Propene (C3H6)
- Butene (C4H8)
- Pentene (C5H10)
- Hexene (C6H12)
- Heptene (C7H14)
- Octene (C8H16)
- Nonene (C9H18)
Here are the molecular formulas and names of the
first ten carbon straight chain
alkynes.
Introduction.
| Name | Molecular Formula |
|---|
| 1-Butyne | C4H6 |
| 1-Pentyne | C5H8 |
| 1-Hexyne | C6H10 |
| 1-Heptyne | C7H12 |
Alkenes are hydrocarbons that contain one or more double bonds, while alkynes contain one or more triple bonds.
Alkenes are relatively stable compounds, but are more reactive than alkanes because of the reactivity of the carbon–carbon π-bond. Most reactions of alkenes involve additions to this π bond, forming new single bonds. Reagents are added through the formation of single bonds to carbon in an addition reaction.
Alkanes are generally unreactive. Alkanes contain only C–H and C–C bonds, which are relatively strong and difficult to break. The similar electronegativities of carbon and hydrogen give molecules which are non-polar.
1) In acid-base reactions, alkynes are the most reactive followed by alkenes and alkanes. This is due to the stability of conjugate base of alkyne by sp hybridized carbon atom. 2)In electrophilic substitution, alkynes are less reactive than alkenes.
The simple answer is none, as alkanes do not engage in hydrogen bonding.
The combination of alkanes with oxygen generating heat is known as combustion. More precisely, combustion is defined as “a chemical reaction with oxygen in which alkane is converted into carbon dioxide and water with the release of heat energy”.
Alkanes are not soluble in water, which is highly polar. The two substances do not meet the criterion of solubility, namely, that “like dissolves like.” Water molecules are too strongly attracted to one another by hydrogen bonds to allow nonpolar alkanes to slip between them and dissolve.
An alcohol is an organic molecule containing an -O-H group. Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding. The hydrogen bonding makes the molecules "stickier", and more heat is necessary to separate them.
Alkanes are non-polar solvents. Since only C and H atoms are present, alkanes are nonpolar. Alkanes consisting of weak dipole dipole bonds can not break the strong hydrogen bond between water molecules hence it is not miscible in water. The same character is also shown by alkenes.
The first four alkanes are methane, ethane, propane, and butane with the Lewis symbols shown below.
The names of all alkanes end with -ane. Alkanes with unbranched carbon chains are simply named by the number of carbons in the chain. The first four members of the series (in terms of number of carbon atoms) are named as follows: CH4 = methane = one hydrogen-saturated carbon.
The bonding in alkanes only consists of σ (sigma) bonds which means they're able to be twisted around. However the pi bond along with the sigma bond in alkenes prevent free rotation. The pi bond occurs due to the side by side overlap of adjacent p orbitals.
The alkanes are a homologous series of hydrocarbons . This means that they have similar chemical properties to each other and they have trends in physical properties. For example, as the chain length increases, their boiling point increases.
Methene is not possible as alkenes require a carbon-carbon double bond and methane only has one carbon atom.
For instance, a bicyclooctane that consists of a six-membered ring and a four-membered ring, which share two adjacent carbon atoms that form a shared edge, is [4.2. 0]-bicyclooctane. That part of the six-membered ring, exclusive of the shared edge has 4 carbons.
Double bonds involving carbon are stronger than single bonds and are also shorter. The bond order is two. Double bonds are also electron-rich, which makes them potentially more reactive in the presence of a strong electron acceptor (as in addition reactions of the halogens).
Alkenes are called unsaturated molecules because two atoms can join onto half of the carbon = carbon double bond when it opens up. Alkenes have two fewer hydrogen atoms than alkanes. Alkanes are described as saturated because they have no C=C double bond and atoms cannot add to them.
Alkynes are hydrocarbons which contain carbon-carbon triple bonds. Their general formula is CnH2n-2 for molecules with one triple bond (and no rings). Alkynes undergo many of the same reactions as alkenes, but can react twice because of the presence of the two p-bonds in the triple bond.
Why are alkane gases like propane so flammable considering that they are non-polar compounds? Polar compounds often have low flash points because of the oxygen, but alkanes have very high heats of combustion, which makes them good fuels even if you have to heat them up a little more before they start burning.
Paraffins is a Latin word meaning (parum = little + affinis = reactivity). Alkanes are called paraffins because they have a little affinity towards a general reagent. In other words, alkanes are inert substances. They undergo reactions under drastic conditions.
The gas burns with a highly-sooty flame, producing thick, black smoke. This happens because of incomplete combustion of the saturated hydrocarbon in the air. The flame is sooty because the percentage of carbon is comparatively higher than that of alkanes and so does not get completely oxidized in air.
In general, alkanes show a relatively low reactivity. Lower alkanes in particular are highly flammable and form explosive mixtures (methane, benzene) with air (oxygen). Solubility of alkanes in water is very low. The physical properties of alkanes follow a similar trend as seen in the regularity of alkane structures.
The structural formulae of methane, ethane and propane shows that they do not have sufficient number of carbon atoms to exist in the form of branched isomer, that is they can be represented in only one way. In other words, branching is not possible in these compounds.
Free rotation is possible around the carbon-carbon single bonds in alkanes, making the carbon chains very flexible and "floppy" — particularly for the larger molecules. Alkanes are nonpolar molecules, since they contain only nonpolar carbon-carbon and carbon-hydrogen bonds.
These are organic molecules that consist only of hydrogen and carbon atoms in a tree-shaped structure (acyclic or not a ring). These are commonly known as paraffins and waxes. Here is a list of the first
10 alkanes.
List the Simplest Hydrocarbons.
| methane | CH4 |
|---|
| ethane | C2H6 |
| propane | C3H8 |
| butane | C4H10 |
| pentane | C5H12 |
Alkanes are nonpolar molecules, since they contain only nonpolar carbon-carbon and carbon-hydrogen bonds. They are therefore not soluble in water, and since they are generally less dense than water, they will float on water (e.g., oil slicks).
Branching decreases the boiling point
So the increase of surface area increases the ability of individual molecules to attract each other. Branching in molecules decreases the surface area thereby decreasing the attractive force between individual molecules. As a result, the boiling point decreases.Hydrocarbons are molecules that contain only carbon and hydrogen. Due to carbon's unique bonding patterns, hydrocarbons can have single, double, or triple bonds between the carbon atoms.
Alkanes are saturated compounds because they have single bond in between C and H. Every C is bounded by 4 H atoms, thus valency of carbon is zero now. Hence they can't react with any other compound until and unless they are changed to alkene or alkyne.
Alkanes are non-polar solvents. Since only C and H atoms are present, alkanes are nonpolar. Alkanes are immiscible in water but freely miscible in other non-polar solvents. Alkanes consisting of weak dipole dipole bonds can not break the strong hydrogen bond between water molecules hence it is not miscible in water.
