The cis and trans forms of a given alkene are different molecules with different physical properties there is a very high energy barrier to rotation about a double bond. Furthermore, many alkenes can take two geometric forms: cis or trans (or Z and E which will be explained in detail in Chapter 7). Ethyne, commonly called acetylene, is used as a fuel in welding blow torches.Īlkenes have trigonal planar electron geometry (due to sp 2 hybrid orbitals at the alkene carbons) while alkynes have linear geometry (due to sp hybrid orbitals at the alkyne carbons). (If you want bananas to ripen quickly, put them in a paper bag along with an apple - the apple emits ethene gas, setting off the ripening process in the bananas). Ethene, the simplest alkene example, is a gas that serves as a cellular signal in fruits to stimulate ripening. Octane, C 8H 18, is a component of gasoline.Īlkenes (sometimes called olefins) have carbon-carbon double bonds, and alkynes have carbon-carbon triple bonds. Some examples of alkanes include methane, CH 4, is the natural gas you may burn in your furnace or on a stove. The simplest functional group in organic chemistry (which is often ignored when listing functional groups) is called an alkane, characterized by single bonds between two carbons and between carbon and hydrogen. Much of the remainder of your study of organic chemistry will be taken up with learning about how the different functional groups tend to behave in organic reactions. For now, we will only worry about drawing and recognizing each functional group, as depicted by Lewis and line structures. Because of their importance in understanding organic chemistry, functional groups have specific names that often carry over in the naming of individual compounds incorporating the groups.Īs we progress in our study of organic chemistry, it will become extremely important to be able to quickly recognize the most common functional groups, because they are the key structural elements that define how organic molecules react. A particular functional group will almost always display its distinctive chemical behavior when it is present in a compound. Gradually they will become familiar, and eventually you will recognize them automatically.įunctional groups are small groups of atoms that exhibit a characteristic reactivity. We expect that you will need to refer back to tables at the end of Section 3.1 quite frequently at first, as it is not really feasible to learn the names and structures of all the functional groups and compound types at one sitting. The concept of functional groups is a very important one. Functional Groups with Single Bonds to Heteroatoms.Molecules with Multiple Functional Groups.Functional Groups with Carbon Single Bonds to other Atoms.When the carbons form a ring they are given the prefix cyclo-.Ĭontinue reading about alkenes and alkynes.\( \newcommand\) The rules for naming branched alkanes are more involved, but are equally systematic (if you wish to learn more about naming branched compounds, consult your textbook). When the carbons are not all in a straight chain, the alkane is said to be branched. The end carbons are bonded to only one carbon, but three hydrogens.
In straight chains, each middle carbon is bonded to two other carbons and two hydrogens. The names shown above correspond to what are called straight chains.
They are named using a prefix that designates the number of carbon atoms in the molecule and the suffix -ane (see below). Hydrocarbons (compounds composed only of carbon and hydrogen) that contain only carbon-carbon single bonds are called alkanes. Structure Example Compound Official Name of Example