Alkanes experience intermolecular van der Waals forces. Stronger intermolecular van der Waals forces give rise to greater boiling points of alkanes. As the boiling point of alkanes is primarily determined by weight, it should not be a surprise that the boiling point has almost a linear relationship with the size molecular weight of the molecule. On the other hand, cycloalkanes tend to have higher boiling points than their linear counterparts due to the locked conformations of the molecules, which give a plane of intermolecular contact. That is, all other things being equal the larger the molecule the higher the melting point. There is one significant difference between boiling points and melting points.
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The more commonly used name for ethyne is acetylene, which used industrially. Rule 1 Find the longest carbon chain that includes both carbons of the triple bond. Rule 2 Number the longest chain starting at the end closest to the triple bond. A 1-alkyne is referred to as a terminal alkyne and alkynes at any other position are called internal alkynes. For example: 4-chlorodiiodomethylnonyne Rule 3 After numbering the longest chain with the lowest number assigned to the alkyne, label each of the substituents at its corresponding carbon.
While writing out the name of the molecule, arrange the substituents in alphabetical order. If there are more than one of the same substituent use the prefixes di, tri, and tetra for two, three, and four substituents respectively.
These prefixes are not taken into account in the alphabetical order. For example: 2,2,triiodomethyldecyne If there is an alcohol present in the molecule, number the longest chain starting at the end closest to it, and follow the same rules. However, the suffix would be —ynol, because the alcohol group takes priority over the triple bond. Number the longest chain starting at the end closest to the triple bond that appears first. The suffix that would be used to name this molecule would be —diyne.
For example: 4-methyl-1,5-octadiyne Substituents containing a triple bond are called alkynyl. For example: 1-chloroethynylbromocyclohexane Here is a table with a few of the alkynyl substituents: Name.
Nomenclature of Alkynes
Higher alkenes and alkynes are named by counting the number of carbons in the longest continuous chain that includes the double or triple bond and appending an -ene alkene or -yne alkyne suffix to the stem name of the unbranched alkane having that number of carbons. The chain is numbered in the direction that gives the lowest number to the first multiply bonded carbon , and adding it as a prefix to the name. Once the chain is numbered with respect to the multiple bond, substituents attached to the parent chain are listed in alphabetical order and their positions identified by number. Compounds that contain two double bonds are classified as dienes , those with three as trienes, and so forth. Dienes are named by replacing the -ane suffix of the corresponding alkane by -adiene and identifying the positions of the double bonds by numerical locants. Double bonds can be incorporated into rings of all sizes, resulting in cycloalkenes.
Nomenclature of Alkenes
Alkane, Alkene, Alkine – was sind die Unterschiede?
IUPAC Nomenclature of Alkanes, Alkenes and Alkynes