Nomenclature: September 2018

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The haloalkanes, also known as alkyl halides, are a group of chemical compounds comprised of an alkane with one or more hydrogens replaced by a halogen atom (fluorine, chlorine, bromine, or iodine). There is a fairly large distinction between the structural and physical properties of haloalkanes and the structural and physical properties of alkanes. As mentioned above, the structural differences are due to the replacement of one or more hydrogens with a halogen atom. The differences in physical properties are a result of factors such as electronegativity, bond length, bond strength, and molecular size.

Alkyl Halide

Alkyl halides are also known as haloalkanes. This page explains what they are and discusses their physical properties. alkyl halides are compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine, bromine or iodine). We will only look at compounds containing one halogen atom. For example:

alkyl halides fall into different classes depending on how the halogen atom is positioned on the chain of carbon atoms. There are some chemical differences between the various types.

Primary alkyl halides

In a primary (1°) halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.Some examples of primary alkyl halides include:

Notice that it doesn't matter how complicated the attached alkyl group is. In each case there is only one linkage to an alkyl group from the CH2 group holding the halogen. There is an exception to this: CH3Br and the other methyl halides are often counted as primary alkyl halides even though there are no alkyl groups attached to the carbon with the halogen on it.

Secondary alkyl halides

In a secondary (2°) halogenoalkane, the carbon with the halogen attached is joined directly to two other alkyl groups, which may be the same or different. Examples:

Tertiary alkyl halides

In a tertiary (3°) halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups, which may be any combination of same or different. Examples:

The Learning Objective is to name halogenated hydrocarbons given formulas and write formulas for these compounds given names.

Many organic compounds are closely related to the alkanes. As we noted in Section 12.7, alkanes react with halogens to produce halogenated hydrocarbons, the simplest of which have a single halogen atom substituted for a hydrogen atom of the alkane. Even more closely related are the cycloalkanes, compounds in which the carbon atoms are joined in a ring, or cyclic fashion.

The reactions of alkanes with halogens produce halogenated hydrocarbons, compounds in which one or more hydrogen atoms of a hydrocarbon have been replaced by halogen atoms:

The replacement of only one hydrogen atom gives an alkyl halide (or haloalkane). The common names of alkyl halides consist of two parts: the name of the alkyl group plus the stem of the name of the halogen, with the ending -ide. The IUPAC system uses the name of the parent alkane with a prefix indicating the halogen substituents, preceded by number indicating the substituent’s location. The prefixes are fluoro-, chloro-, bromo-, and iodo-. Thus CH3CH2Cl has the common name ethyl chloride and the IUPAC name chloroethane. Alkyl halides with simple alkyl groups (one to four carbon atoms) are often called by common names. Those with a larger number of carbon atoms are usually given IUPAC names.

Alkyne Naming Roles

Naming Alkynes

Like previously mentioned, the IUPAC rules are used for the naming of alkynes.

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-chloro-6-diiodo-7-methyl-2-nonyne

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:

2,2,10-triiodo-5-methyldec-3-yne_new_301.png

2,2,10-triiodo-5-methyl-3-decyne

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.

5- methyl-7-octyn-3-ol

When there are two triple bonds in the molecule, find the longest carbon chain including both the triple bonds. 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

Rule 4

Substituents containing a triple bond are called alkynyl. For example:

1-chloro-1-ethynyl-4-bromocyclohexane

Here is a table with a few of the alkynyl substituents:

Name	Molecule
Ethynyl	-C?CH
2- Propynyl	-CH2C?CH
2-Butynyl	-CH3C?CH2CH3

Rule 5

A molecule that contains both double and triple bonds is called an alkenyne. The chain can be numbered starting with the end closest to the functional group that appears first. For example:

6-ethyl-3-methyl-1,4-nonenyne

Reference

Vollhardt, Peter, and Neil E. Schore. Organic Chemistry: Structure and Function. 5th Edition. New York: W. H. Freeman & Company, 2007.

Problems

Name or draw out the following molecules:

1. 4,4-dimethyl-2-pentyne

2. 4-Penten-1-yne

3. 1-ethyl-3-dimethylnonyne

Alkyne 1

Introduction

Here are the molecular formulas and names of the first ten carbon straight chain alkynes.

Name	Molecular Formula
Ethyne	C2H2
Propyne	C3H4
1-Butyne	C4H6
1-Pentyne	C5H8
1-Hexyne	C6H10
1-Heptyne	C7H12
1-Octyne	C8H14
1-Nonyne	C9H16
1-Decyne	C10H18

The more commonly used name for ethyne is acetylene, which used industrially.

Alkyne

Alkynes are organic molecules made of the functional group carbon-carbon triple bonds and are written in the empirical formula of

C_{n} H_{2 n - 2}

. They are unsaturated hydrocarbons. Like alkenes have the suffix –ene, alkynes use the ending –yne; this suffix is used when there is only one alkyne in the molecule. If a molecule contains both a double and a triple bond, the carbon chain is numbered so that the first multiple bond gets a lower number. If both bonds can be assigned the same number, the double bond takes precedence. The molecule is then named "n-ene-n-yne", with the double bond root name preceding the triple bond root name (e.g. 2-hepten-4-yne).

Alkane 3

Note that the numbering of "2-4" above yields a molecule with two double bonds separated by just one single bond. Double bonds in such a condition are called "conjugated", and they represent an enhanced stability of conformation, so they are energetically favored as reactants in many situations and combinations.

Alkane	CnH2n+2	This is the maximum H/C ratio for a given number of carbon atoms.
Alkene	CnH2n	Each double bond reduces the number of hydrogen atoms by 2.

The parent structure is the longest chain containing both carbon atoms of the double bond. The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120° A double bond consists of one sigma bond formed by overlap of sp2 hybrid orbitals and one pi bond formed by overlap of parallel 2 p orbitals

Figure 1: (a) The σ-bonded framework is formed by the overlap of two sets of singly occupied carbon sp2 hybrid orbitals and four singly occupied hydrogen 1s orbitals to form electron-pair bonds. This uses 10 of the 12 valence electrons to form a total of five σ bonds (four C–H bonds and one C–C bond). (b) One singly occupied unhybridized 2pz orbital remains on each carbon atom to form a carbon–carbon π bond. (Note: by convention, in planar molecules the axis perpendicular to the molecular plane is the z-axis.)

The molecular formula of a hydrocarbon provides information about the possible structural types it may represent. For example, consider compounds having the formula C5H8. The formula of the five-carbon alkane pentane is C5H12 so the difference in hydrogen content is 4. This difference suggests such compounds may have a triple bond, two double bonds, a ring plus a double bond, or two rings. Some examples are shown here, and there are at least fourteen others!

IUPAC Rules for Alkene and Cycloalkene Nomenclature

The ene suffix (ending) indicates an alkene or cycloalkene.
The longest chain chosen for the root name must include both carbon atoms of the double bond.
The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
Substituent groups containing double bonds are:

H2C=CH– Vinyl group

H2C=CH–CH2– Allyl group

Alkane 2

Introduction

Alkenes and alkynes are hydrocarbons which respectively have carbon-carbon double bond and carbon-carbon triple bond functional groups. The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups. Alkenes are named as if they were alkanes, but the "-ane" suffix is changed to "-ene". If the alkene contains only one double bond and that double bond is terminal (the double bond is at one end of the molecule or another) then it is not necessary to place any number in front of the name.

butane: C4H10 (CH3CH2CH2CH3)
butene: C4H8 (CH2=CHCH2CH3)

If the double bond is not terminal (if it is on a carbon somewhere in the center of the chain) then the carbons should be numbered in such a way as to give the first of the two double-bonded carbons the lowest possible number, and that number should precede the "ene" suffix with a dash, as shown below.

correct: pent-2-ene (CH3CH=CHCH2CH3)
incorrect: pent-3-ene (CH3CH2CH=CHCH3)
The second one is incorrect because flipping the formula horizontally results in a lower number for the alkene.

If there is more than one double bond in an alkene, all of the bonds should be numbered in the name of the molecule - even terminal double bonds. The numbers should go from lowest to highest, and be separated from one another by a comma. The IUPAC numerical prefixes are used to indicate the number of double bonds.

octa-2,4-diene: CH3CH=CHCH=CHCH2CH2CH3
deca-1,5-diene: CH2=CHCH2CH2CH=CHCH2CH2CH2CH3

Alkane 1

- Alkenes contain carbon-carbon double bonds and are unsaturated hydrocarbons with the molecular formula is CnH2n. This is also the same molecular formula as cycloalkanes. Alkenes are named using the same general naming rules for alkanes, except that the suffix is now -ene. There are a few other small differences:

The main chain of carbon atoms must contain both carbons in the double bond. The main chain is numbered so that the double bond gets the smallest number.
Before the root name, the number of the carbon atom at which the double bond starts (the smaller number) is written.
If more than one double bond is present, the prefixes di-, tri-, tetra-, etc. are used before the -ene, and (strangely) the letter "a" is added after the prefix for the number of carbon atoms.

Alkene Full

Alkenes contain carbon-carbon double bonds and are unsaturated hydrocarbons with the molecular formula is CnH2n. This is also the same molecular formula as cycloalkanes. Alkenes are named using the same general naming rules for alkanes, except that the suffix is now -ene. There are a few other small differences:

The main chain of carbon atoms must contain both carbons in the double bond. The main chain is numbered so that the double bond gets the smallest number.
Before the root name, the number of the carbon atom at which the double bond starts (the smaller number) is written.
If more than one double bond is present, the prefixes di-, tri-, tetra-, etc. are used before the -ene, and (strangely) the letter "a" is added after the prefix for the number of carbon atoms.

Introduction

butane: C4H10 (CH3CH2CH2CH3)
butene: C4H8 (CH2=CHCH2CH3)

correct: pent-2-ene (CH3CH=CHCH2CH3)
incorrect: pent-3-ene (CH3CH2CH=CHCH3)
The second one is incorrect because flipping the formula horizontally results in a lower number for the alkene.

octa-2,4-diene: CH3CH=CHCH=CHCH2CH2CH3
deca-1,5-diene: CH2=CHCH2CH2CH=CHCH2CH2CH2CH3

Alkane	CnH2n+2	This is the maximum H/C ratio for a given number of carbon atoms.
Alkene	CnH2n	Each double bond reduces the number of hydrogen atoms by 2.

IUPAC Rules for Alkene and Cycloalkene Nomenclature

The ene suffix (ending) indicates an alkene or cycloalkene.
The longest chain chosen for the root name must include both carbon atoms of the double bond.
The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
Substituent groups containing double bonds are:

H2C=CH– Vinyl group
H2C=CH–CH2– Allyl group

EXAMPLE 1

In this diagram this is a cis conformation. It has both the substituents going upward. This molecule would be called (cis) 5-chloro-3-heptene.)

Trans would look like this

v. On the other hand if there are 3 or 4 non-hydrogen different atoms attached to the alkene then use the E, Z system.

E (entgegen) means the higher priority groups are opposite one another relative to the double bond.

Z (zusammen) means the higher priority groups are on the same side relative to the double bond.

(You could think of Z as Zame Zide to help memorize it.)

EXAMPLE 2

Solution

In this example it is E-4-chloro-3-heptene. It is E because the Chlorine and the CH2CH3 are the two higher priorities and they are on opposite sides.

vi. A hydroxyl group gets precedence over th double bond. Therefore alkenes containing alchol groups are called alkenols. And the prefix becomes --enol. And this means that now the alcohol gets lowest priority over the alkene.

vii. Lastly remember that alkene substituents are called alkenyl. Suffix --enyl.

Here is a chart containing the systemic name for the first twenty straight chain alkenes.

Name	Molecular formula
Ethene	C2H4
Propene	C3H6
Butene	C4H8
Pentene	C5H10
Hexene	C6H12
Heptene	C7H14
Octene	C8H16
Nonene	C9H18
Decene	C10H20
Undecene	C11H22
Dodecene	C12H24
Tridecene	C13H26
Tetradecene	C14H28
Pentadecene	C15H30
Hexadecene	C16H32
Heptadecene	C17H34
Octadecene	C18H36
Nonadecene	C19H38
Eicosene	C20H40

Did you notice how there is no methene? Because it is impossible for a carbon to have a double bond with nothing.

Geometric Isomers

Double bonds can exist as geometric isomers and these isomers are designated by using either the cis / trans designation or the modern E / Z designation.

cis Isomers

.The two largest groups are on the same side of the double bond.

trans Isomers

...The two largest groups are on opposite sides of the double bond.

E/Z nomenclature

E = entgegan ("trans") Z = zusamen ("cis")

Priority of groups is based on the atomic mass of attached atoms (not the size of the group). An atom attached by a multiple bond is counted once for each bond.

fluorine atom > isopropyl group > n-hexyl group

deuterium atom > hydrogen atom

-CH2-CH=CH2 > -CH2CH2CH3

EXAMPLE 3

Try to name the following compounds using both conventions...

Common names

Remove the -ane suffix and add -ylene. There are a couple of unique ones like ethenyl's common name is vinyl and 2-propenyl's common name is allyl. That you should know are...

vinyl substituent H2C=CH-
allyl substituent H2C=CH-CH2-
allene molecule H2C=C=CH2
isoprene

Endocyclic Alkenes

Endocyclic double bonds have both carbons in the ring and exocyclic double bonds have only one carbon as part of the ring.

Cyclopentene is an example of an endocyclic double bond.

Methylenecylopentane is an example of an exocyclic double bond.

Name the following compounds...

1-methylcyclobutene. The methyl group places the double bond. It is correct to also name this compound as 1-methylcyclobut-1-ene.

1-ethenylcyclohexene, the methyl group places the double bond. It is correct to also name this compound as 1-ethenylcyclohex-1-ene. A common name would be 1-vinylcyclohexene.

Try to draw structures for the following compounds...

2-vinyl-1,3-cyclohexadiene

Nomenclature

Etea Result

Mdcat Result 2018

Alkyl Halide (Examples)

Alkyl Halide

Primary alkyl halides

Secondary alkyl halides

Tertiary alkyl halides

Alkyne Naming Roles

Naming Alkynes

Rule 1

Rule 2

Rule 3

Rule 4

Rule 5

Reference

Problems

Alkyne 1

Introduction

Alkyne

Alkane 3

IUPAC Rules for Alkene and Cycloalkene Nomenclature

Alkane 2

Introduction

Alkane 1

Alkene Full

Introduction

IUPAC Rules for Alkene and Cycloalkene Nomenclature

Geometric Isomers

cis Isomers

trans Isomers

E/Z nomenclature

Common names

Endocyclic Alkenes

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