Naming Other Substituents: Study with Video Lessons, Practice Problems & Examples

An alkyl halide consists of an alkyl group bonded to a halogen, which acts as a substituent in organic compound naming. Halogens are named as Fluoro, Chloro, Bromo, and Iodo, with their positions indicated numerically. A phenyl group, derived from benzene (C₆H₆), serves as a substituent by removing one hydrogen, resulting in C₆H₅. This group can attach to longer carbon chains, and its naming follows the location of the phenyl group and the parent chain name.

Alkyl Halides Concept 1

So remember that an alkyl halide is just an alkyl group connected to a halogen. Here we're going to say that halogens attached to a carbon chain are named as substituents. Fluorine as a substituent is called Fluoro, Chlorine is called Chloro, Bromine is called Bromo, Iodine is called Iodo. In terms of our naming convention, they're acting as substituents, so we'd have to give their numerical location in terms of our parent chain. They are substituents with these names, and then we have to worry about what is the parent chain. Is it a 6 membered chain? Is it cyclic? Etcetera. So just remember, when it comes to naming organic compounds, these halogens serve as substituents, and as substituents they're given these new names.

Alkyl Halides Example 1

Here it says, determine the systematic name of the following alkane. Our job is first to find the longest carbon chain, which represents our parent chain. We're utilizing steps 1 to 6. Remember, we're utilizing the rules that we learned in terms of naming alkanes with substituents. You have to watch those videos, make sure you go back and take a look at those 6 steps. So here, 1, 2, 3, 4, 5, 6, 7, 8, 9. 9 seems to be the longest chain that we can have in terms of this alkane. So that is our parent chain. We'll highlight it for ourselves.

Now remember, we number from the end closest to a substituent. Here we have a 3 carbon substituent, a 1 carbon substituent, and bromine. 1, 2, 3, 4 to get to this 3 carbon substituent. Or 1, 2, 3 to get to the bromine substituent. We number it from the end closest to a substituent, so we're going to number it from the right side. So, 1, 2, 3, 4, 5, 6, 7, 8, 9. 9 carbons means that our alkane is nonane. Now, about our substituents. A 3 carbon substituent with the bond on the middle, carbon means that this is isopropyl. A one carbon substituent would be methyl, and then bromine is termed bromo.

Remember we basically name, we number these for their location, and we write them alphabetically. B comes before I, I comes before M. So we start out with 3-bromo-6-isopropyl-5-methyl nonane. This would be the name of this particular alkane compound. Here we have the introduction of our halogen bromine group, which is listed as bromo.

Name the following compound.

• A. 3-fluoro-1-ethylpentane
• B. 3-fluoro-1-ethylcyclopentane
• C. 1-ethyl-3-fluorocyclopentane
• D. 1-ethyl-4-fluorocyclopentane

Phenyl Group Concept 2

In this video, we're going to talk about the phenyl group. Now a phenyl group is just basically a benzene ring as a substituent on a parent chain. Now here, the parent chain can be an alkane, an alkene, an alkyne, as long as it's longer than 6 carbons. Remember the formula for benzene is C6H6. But since it's acting as a substituent, we're going to deduct away a hydrogen. So here it becomes C6H5 connected to something else, a longer chain that's an alkane, alkene, or an alkyne. Now, this is its condensed formula, if we wanted to look at its skeletal formula, remember Benzene looks like this, it's a 6 membered ring with alternating double and single bonds. 5 of the carbons have a hydrogen, the 6th one, remember we took away its hydrogen so it can serve as a substituent or branch group, connected to something larger than itself. Because it is a substituent, the naming convention is the location of the Phenyl group, and then the Parent Chain Name. So keep this in mind. Benzene, when it becomes a substituent, we call it Phenyl.

Phenyl Group Example 2

So here we need to determine a systematic name of the following alkane. Here, our carbon chain is this portion here, because it's composed of 1, 2, 3, 4, 5, 6, 7, 8 carbons. Remember, as long as our carbon chain has more than 6 carbons, it becomes the parent chain, and benzene becomes a substituent. And then, besides that benzene, we have these 2 carbon substituents which are methyl groups. Now remember, we number it from the end closest to a substituent. We'd number this end as 1 because on carbon number 1, we immediately have a substituent in the form of Benzene. So 1, 2, 3, 4, 5, 6, 7, 8. And the carbon chain is octane. Benzene as a substituent is phenyl, and then we have methyl groups on carbon number 5. Now, we name substituents alphabetically, M comes before P, so those 2 methyl groups are on 5. So we have to list 5 twice. Because if you just said 5-dimethyl, all I would know is that one of the methyl groups is on carbon number 5, but where is the other one? So we have to say 5,5 to say that both of them are on that carbon number 5. So 5,5, there are 2 identical substituents, so we use the numerical prefix di-methyl 1-phenyl-octane. This will be the name of my alkane compound.

Draw a structure for the following alkane: 3-tert-butyl-1-phenylheptane.

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is an alkyl halide and how are halogens named as substituents?

An alkyl halide is an organic compound where an alkyl group is bonded to a halogen. In naming these compounds, halogens are treated as substituents. The names for halogens as substituents are: Fluorine (Fluoro), Chlorine (Chloro), Bromine (Bromo), and Iodine (Iodo). When naming, you must indicate the numerical position of the halogen on the carbon chain. For example, in 2-chloropropane, the chlorine is attached to the second carbon of a three-carbon chain.

How do you name a compound with a phenyl group as a substituent?

A phenyl group is a benzene ring (C₆H₅) acting as a substituent. When naming a compound with a phenyl group, you need to specify the location of the phenyl group on the parent chain. For example, in 3-phenylhexane, the phenyl group is attached to the third carbon of a six-carbon chain. The parent chain can be an alkane, alkene, or alkyne, as long as it is longer than six carbons.

What is the difference between a phenyl group and a benzene ring?

A benzene ring is a six-carbon ring with alternating double and single bonds, having the formula C₆H₆. A phenyl group is derived from benzene by removing one hydrogen atom, resulting in C₆H₅. The phenyl group acts as a substituent attached to a larger carbon chain, whereas benzene is a standalone molecule.

How do you determine the parent chain when naming compounds with substituents?

To determine the parent chain, identify the longest continuous carbon chain in the molecule. This chain serves as the base name of the compound. Number the chain from the end nearest a substituent to give the substituents the lowest possible numbers. For example, in 4-bromo-2-methylhexane, the parent chain is hexane (six carbons), and the substituents are bromo and methyl, located at positions 4 and 2, respectively.

Why is the numerical location of substituents important in organic compound naming?

The numerical location of substituents is crucial because it provides a clear and unambiguous description of the compound's structure. It ensures that each substituent is correctly positioned on the parent chain, which is essential for identifying and differentiating between similar compounds. For example, 2-chloropropane and 1-chloropropane are different compounds with chlorine attached to different carbons.