Alkoxy Group Overview and Examples

Maram Ghadban, Danielle Reid
  • Author
    Maram Ghadban

    A freelance tutor equipped with a bachelor's of science in chemical engineering. Graduated from the American University of the Middle East with a GPA of 3.87, performed a number of scientific primary and secondary research. Tutored university level students in various courses in chemical engineering, math, and art. Has experience tutoring middle school and high school level students in science courses.

  • Instructor
    Danielle Reid

    Danielle has taught middle school science and has a doctorate degree in Environmental Health

Explore the alkoxy functional group. Learn what the alkoxy group is. Review its general formula and examples. Explore the alkyl group list to name the alkoxy group. Updated: 01/31/2022

Alkoxy Group

An alkoxy group is a functional group whose primary constituents are oxygen, carbons, and hydrogens. A functional group is a chemical substituent that is attached to the main organic chain. It is a characteristic substituent that is made of different molecules attached to the organic carbon backbone. It carries the chemical properties of the organic molecule, which is why organic compounds are classified according to their functional groups. The alkoxy group is composed of an oxygen atom attached to an organic carbon chain. The word alkoxy combines two different terms:

  • The word alk- is derived from the word alkyl.
  • The word -oxy is derived from oxygen.

The general formula for the alkoxy group is {eq}-OR {/eq}, where R is the alkyl group, which is a hydrocarbon chain that is solely made of carbon and hydrogen atoms. The oxygen atom forms a single covalent bond with the carbon in the alkyl group. The alkoxy functional group is alternatively known as the alkyloxy group.

Alkyl Group List

The alkyl group is one of the two main constituents of the alkoxy group. It is an organic carbon chain that is made of nothing but carbon and hydrogen atoms. The absence of atoms different from C and H is the reason the alkyl group is classified as a hydrocarbon substituent. The alkyl group list is documented in Table 1, which shows the names of the alkyl groups and their corresponding chemical formulas.

All Things Alkoxy: An Overview

What do methoxy, ethyoxy, and alkyloxy all have in common? Besides the tongue twisting nature of pronouncing each name, they are all examples of alkoxy groups. An alkoxy group is an organic functional group that contains an alkyl group attached to an oxygen atom.

I know you are probably thinking, what an overloaded definition! Well, an organic functional group is the portion of a chemical compound that is a recognizable (or classifiable) group. Shown below is a table of very common functional groups. Do you see the alkyl group? An alkyl group contains only carbon and hydrogen atoms.

Examples of Different Functional Groups
table 1

The molecular formula for an alkoxy group is R-O. 'R' represents the alkyl group that is attached to the oxygen atom. Going back to our definition, we can see that alkoxy is a type of functional group because we can identify the alkyl portion in its molecular formula.

Naming alkoxy groups is a very easy process. But to understand naming we need to revisit our friend, the alkyl group. When naming a compound that contains an alkyl group, you must first determine how many carbon atoms are present in a linear chain. This number corresponds to the prefix within the chemical name. A list of common prefixes is shown below. To complete the name, you add the suffix '-yl' to the prefix.

For example, if a compound has a linear chain of five carbon atoms, this corresponds to the prefix 'penta.' Adding the suffix '-yl,' this alkyl group would be named pentyl. We follow a similar process when naming alkoxy groups. The only exception is a change to the suffix ending, where you add '-oxy' to the prefix as opposed to '-yl.'

Table 1: Names of Alkyl Groups
Alkyl Group Chemical Formula No. of C atoms
Methyl -CH3 1
Ethyl -CH2CH3 2
Propyl -(CH2)2CH3 3
Butyl -(CH2)3CH3 4
Pentyl -(CH2)4CH3 5
Hexyl -(CH2)5CH3 6
Heptyl -(CH2)6CH3 7
Octyl -(CH2)7CH3 8
Nonyl -(CH2)8CH3 9
Decyl -(CH2)9CH3 10

Examples of Alkoxy Group Attached to Compounds

The alkoxy group {eq}-OR {/eq} is a functional group, which means it is not observed as an independent organic molecule, but a substituent that is attached an organic compound. Figure 1 and Figure 2 show examples of compounds that contain the alkoxy group.


Figure 1: An ethoxy group is attached to the benzene ring (left), a propoxy group is attached to the pentane chain (right).

Compounds with alkoxy functional group



Figure 2: A methoxy group is attached to the cyclohexane ring (left), a propoxy group is attached to hexanol (right).

Compounds with alkoxy functional group


The compound in the right side of Figure 1 is an ether. The oxygen atom separates the parent alkyl chain from the alkyl in the alkoxy group. The reason the smaller alkyl chain was selected to be a part of the alkoxy group is because the R in the alkoxy group must always be smaller than the R in the parent chain. The number of carbons in the parent chain must always be larger than the number of carbons in a substituent.

The figures show that the alkoxy group can be attached to different compounds; it can be attached to an aromatic ring (Figure 1, left), an aliphatic chain (Figure 1, right), a cyclic compound (Figure 2, left), and even a compound with a different functional group (Figure 2, right).

Naming Alkoxy Group

The naming of alkoxy groups is done by simply counting the number of carbons in the alkyl chain, assigning the correct prefix, then adding the suffix -oxy. Table 2 shows the prefixes and the corresponding number of carbon atoms. If the alkyl part was composed of 7 carbon atoms, the prefix hept- is used. Combining the prefix hept- with the suffix -oxy gives "heptoxy." An alkoxy group made of 7 carbon atoms is called heptoxy. An alkoxy group that is made of 5 carbon atoms is called pentoxy.

To differentiate between the alkane parent chain and the alkyl in the alkoxy functional group:

  • Count the number of carbon atoms in each alkyl group. The alkyl groups are segregated by an oxygen atom.
  • The larger alkyl group is the parent chain. The smaller alkyl group is a part of the alkoxy {eq}-OR {/eq} group.

Figure 3 shows an example of an alkoxy group attached to a regular alkane chain. The parent chain is the alkyl group that is made of a larger number of carbons. The alkyl group is made of three carbons, while the alkane in the parent chain is made of four carbons. The alkoxy group in this molecule is propoxy {eq}CH_3CH_2CH_2O- {/eq} and not butoxy {eq}CH_3CH_2CH_2CH_2O- {/eq}.


Figure 3: The R of the alkoxy group is always the alkyl group that is made of a smaller number of carbon atoms.

Naming of alkoxy group


Table 2: Prefixes in Organic Chemistry
Prefix No. C Atoms Alkoxy Group Name
Meth- 1 Methoxy
Eth- 2 Ethoxy
Prop- 3 Propoxy
But- 4 Butoxy
Pent- 5 Pentoxy
Hex- 6 Hexoxy
Hept- 7 Heptoxy
Oct- 8 Octoxy
Non- 9 Nonoxy
Dec- 10 Decoxy

Reactions of Alkoxy Group Compounds

Compounds with an alkoxy group undergo various chemical reactions. The alkoxy group in these compounds participate in reactions where the following compounds are formed:

  • Alcohols, which are organic molecules that contain at least one hydroxyl group {eq}-OH {/eq}.
  • Ethers, which are organic molecules with the structural formula {eq}R-O-R {/eq}. Their functional group is the alkoxy group. The alkoxy group can be attached to an alkyl or an aryl group. An aryl group is a cyclic aromatic ring that is characterized by having conjugated double bonds. An example of such is the benzene ring.
  • Alkoxide ions, which are organic carbon atoms bonding to a negatively charged oxygen atom.

Common Prefixes Used In Organic Nomenclature
table 2

Alkoxy Groups as the Reactant and Product

The alkoxy group is commonly formed as a fragment from chemical compounds. In particular, this fragment arises when a chemical compound undergoes a reaction resulting in the removal of its hydrogen atom. In order to form an alkoxy group, this hydrogen atom must be attached to an oxygen atom. The illustration shown below describes how an alkoxy group can be formed from alcohol.

Example of an Alkoxy Formation From an Alcohol
example

Just as an alkoxy group is formed (i.e. becoming a product), it is also used to create other compounds (i.e. acting as a reactant). There are three compounds in particular: alcohol, ether, and the alkoxide ion. In a reversal of the equation shown above, alkoxy groups can bind to a hydrogen atom and form alcohol compounds. Ether compounds are formed when an alkoxy group binds to another alkyl group. Lastly, an alkoxy group carrying a negative charge is known as an alkoxide ion. Whether the alkoxy group is the reactant or the product, if you know how to spot its molecular formula (R-O) identifying alkoxy is easy to do.

Spotting an Alkoxy Group: Examples

There are a wide variety of alkoxy groups. Remember our friends methoxy, ethyoxy, and alkyloxy? We can classify them as alkoxy groups. Let's look at a few chemical compounds using the examples shown below. As a tip, always look for the oxygen atom first within the structure. Think of the oxygen atom as your compass guiding you towards finding and determining the location of the alkoxy group.

Example #1: Methoxyethane

Example One of a Compound Containing an Alkoxy Group
example 1

Locating the oxygen atom, you will see that it is bonded to a Ch3 (methyl) and Ch2Ch3 (ethyl). However, the chemical name provides a hint about where the alkoxy group is located in the structure. The term, 'methoxy-' tells you that the alkoxy group corresponds to the oxygen atom bonded to the Ch3. Don't be afraid to use the chemical name as a reference when locating alkoxy groups, if possible.

Example #2: 3-isopropoxy-1-butanol

Example Two of a Compound Containing an Alkoxy Group
example

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Additional Info

All Things Alkoxy: An Overview

What do methoxy, ethyoxy, and alkyloxy all have in common? Besides the tongue twisting nature of pronouncing each name, they are all examples of alkoxy groups. An alkoxy group is an organic functional group that contains an alkyl group attached to an oxygen atom.

I know you are probably thinking, what an overloaded definition! Well, an organic functional group is the portion of a chemical compound that is a recognizable (or classifiable) group. Shown below is a table of very common functional groups. Do you see the alkyl group? An alkyl group contains only carbon and hydrogen atoms.

Examples of Different Functional Groups
table 1

The molecular formula for an alkoxy group is R-O. 'R' represents the alkyl group that is attached to the oxygen atom. Going back to our definition, we can see that alkoxy is a type of functional group because we can identify the alkyl portion in its molecular formula.

Naming alkoxy groups is a very easy process. But to understand naming we need to revisit our friend, the alkyl group. When naming a compound that contains an alkyl group, you must first determine how many carbon atoms are present in a linear chain. This number corresponds to the prefix within the chemical name. A list of common prefixes is shown below. To complete the name, you add the suffix '-yl' to the prefix.

For example, if a compound has a linear chain of five carbon atoms, this corresponds to the prefix 'penta.' Adding the suffix '-yl,' this alkyl group would be named pentyl. We follow a similar process when naming alkoxy groups. The only exception is a change to the suffix ending, where you add '-oxy' to the prefix as opposed to '-yl.'

Common Prefixes Used In Organic Nomenclature
table 2

Alkoxy Groups as the Reactant and Product

The alkoxy group is commonly formed as a fragment from chemical compounds. In particular, this fragment arises when a chemical compound undergoes a reaction resulting in the removal of its hydrogen atom. In order to form an alkoxy group, this hydrogen atom must be attached to an oxygen atom. The illustration shown below describes how an alkoxy group can be formed from alcohol.

Example of an Alkoxy Formation From an Alcohol
example

Just as an alkoxy group is formed (i.e. becoming a product), it is also used to create other compounds (i.e. acting as a reactant). There are three compounds in particular: alcohol, ether, and the alkoxide ion. In a reversal of the equation shown above, alkoxy groups can bind to a hydrogen atom and form alcohol compounds. Ether compounds are formed when an alkoxy group binds to another alkyl group. Lastly, an alkoxy group carrying a negative charge is known as an alkoxide ion. Whether the alkoxy group is the reactant or the product, if you know how to spot its molecular formula (R-O) identifying alkoxy is easy to do.

Spotting an Alkoxy Group: Examples

There are a wide variety of alkoxy groups. Remember our friends methoxy, ethyoxy, and alkyloxy? We can classify them as alkoxy groups. Let's look at a few chemical compounds using the examples shown below. As a tip, always look for the oxygen atom first within the structure. Think of the oxygen atom as your compass guiding you towards finding and determining the location of the alkoxy group.

Example #1: Methoxyethane

Example One of a Compound Containing an Alkoxy Group
example 1

Locating the oxygen atom, you will see that it is bonded to a Ch3 (methyl) and Ch2Ch3 (ethyl). However, the chemical name provides a hint about where the alkoxy group is located in the structure. The term, 'methoxy-' tells you that the alkoxy group corresponds to the oxygen atom bonded to the Ch3. Don't be afraid to use the chemical name as a reference when locating alkoxy groups, if possible.

Example #2: 3-isopropoxy-1-butanol

Example Two of a Compound Containing an Alkoxy Group
example

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Frequently Asked Questions

What is the alkoxy functional group?

An alkoxy functional group is a substituent that is made of an oxygen atom that is bonded to an alkyl chain R. The general formula for an alkoxy group is -OR.

How do you name an alkoxy group?

The first step in naming an alkoxy group is recognizing the alkyl chain and assigning the correct prefix for the alkyl group. The alkyl prefix relates to the number of carbon atoms that make the alkyl chain. If there were were 5 carbons, then the prefix pent- is used. If there were 6 carbons, then the prefix hex- is used. After assigning the prefix, combine it with the suffix -oxy. Example: pentoxy, hexoxy.

Is ethoxy a functional group?

Ethoxy is an alkoxy functional group. The prefix eth- indicates that there are two carbon atoms in the alkyl part R in alkoxy. This means that the chemical formula for an ethoxy functional group is CH3CH2O-.

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