Secondary sp3 hybridized carbons

[Lunasly]

For those of you who have BR, question 1.7 on page 21 asks which carbon-carbon single bond is the MOST stable according to the table of bond dissociation energies provided.

I don't have an issue picking out the correct answer, but one part of the answer explanation seemed odd. Answer choice B, C, and D all include a secondary sp3 hybridized carbon bonded to another carbon (the other carbon is irrelevant to my question). According to the answer explanation and the table provided, a secondary carbon could arise from a group such as ethyl or n-propyl. However, considering that only Et is listed as a substituent in the table, it's the only one we can use. I don't understand how to read this table. How does it account for adding multiple substituents to the carbon we are interested in? For instance, one of the answer choices is an sp2 hybridized carbon (e.g., from a vinyl group) bonded to a secondary sp3 hybridized carbon atom (e.g., which arises from an ethyl group???? how???).

Thanks for the help.

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[Chrisz]

I do not quite understand your question? I guess you are asking why u should pick ethyl group? Becasue it says "secondary" sp3 carbon. secondary means this carbon is connected to two carbons. an ethyl group carbon is connected to one carbon by itself, so when it connects to the sp2 carbon, it is conneted to 2 carbons. Then, it becomes a secondary carbon. Is this what you asking for. Actually, we do not need to use the table to solve this question. sp2 is more stable than sp3, so C and D are eliminated. More substituted radical is more stable, so comparatively lower in energy than less substituted radicals, which means B is eliminated. So A is the Answer

 

[Lunasly]

I do not quite understand your question? I guess you are asking why u should pick ethyl group? Becasue it says "secondary" sp3 carbon. secondary means this carbon is connected to two carbons. an ethyl group carbon is connected to one carbon by itself, so when it connects to the sp2 carbon, it is conneted to 2 carbons. Then, it becomes a secondary carbon. Is this what you asking for. Actually, we do not need to use the table to solve this question. sp2 is more stable than sp3, so C and D are eliminated. More substituted radical is more stable, so comparatively lower in energy than less substituted radicals, which means B is eliminated. So A is the Answer

 

[Lunasly]

By that logic, why can't I just add a methyl group then? The carbon of interest would still be bonded to the vinylic carbon and a carbon of a methyl group, making it secondary. How does specifically adding an ethyl group make the carbon secondary? Or does that column not indicate an ethyl group is being added, but that the carbon of interest is bonded to 2 carbons?

 

[Chrisz]

By that logic, why can't I just add a methyl group then? The carbon of interest would still be bonded to the vinylic carbon and a carbon of a methyl group, making it secondary. How does specifically adding an ethyl group make the carbon secondary? Or does that column not indicate an ethyl group is being added, but that the carbon of interest is bonded to 2 carbons?

Bro, no offence, you really have to work on some terminologies. Primary carbon means the carbon of interest connects directly to one carbon, secondary means the carbon of interest connects two carbons, tertiary means three. if you add methyl carbon to the vinyllic carbon, the methyl carbon becomes primary sp3 carbon, not secondary. so any carbon that bonds to another carbon already will become secondary once added to the vinyllic carbon. By this definition, ethyl satisfies the condition.

 

[Lunasly]

b'm well aware of the terminology, but I can't seem to grasp an understanding of how these atoms are bonding to one another. Let me get this straight, if I have a vinylic carbon (the first carbon of interest) forming a single bond to another carbon (the second carbon of intetest) with three hydrogen atoms, then the second carbon of interest is primary because it is bonded to only one other carbon (the vinylic carbon). However, if I add an ethyl group to the vinylic carbon, then the second carbon of interest is now secondary because it has two carbons attached. Where I think I am getting confused is whether or not the bonding of the carbon of interest to the vinylic carbon counts. Because if I have a central carbon bonded to 4 other methyl groups, what is that called? I'm assuming that by this logic, it can't be tertiary because it has more than three carbons bonded to it.

Thanks for the help.

 

[Chrisz]

One thing to make sure primary, secondary, and tertiary are used to describe sp3 carbons, which means to describe carbons "single-bonded" to 4 other atoms. Vinylic carbons are sp2 hybridized, so vinylic carbons are double bonded, so they can't bond to 4 other atoms. Primary, sec, ter...are all reserved for sp3 carbons. In the case, an sp3 carbon bonding to 4 other carbons, it is called quarternary carbons

 

[Chrisz]

b'm well aware of the terminology, but I can't seem to grasp an understanding of how these atoms are bonding to one another. Let me get this straight, if I have a vinylic carbon (the first carbon of interest) forming a single bond to another carbon (the second carbon of intetest) with three hydrogen atoms, then the second carbon of interest is primary because it is bonded to only one other carbon (the vinylic carbon). However, if I add an ethyl group to the vinylic carbon, then the second carbon of interest is now secondary because it has two carbons attached. Where I think I am getting confused is whether or not the bonding of the carbon of interest to the vinylic carbon counts. Because if I have a central carbon bonded to 4 other methyl groups, what is that called? I'm assuming that by this logic, it can't be tertiary because it has more than three carbons bonded to it.

Thanks for the help.

One thing to make sure primary, secondary, and tertiary are used to describe sp3 carbons, which means to describe carbons "single-bonded" to 4 other atoms. Vinylic carbons are sp2 hybridized, so vinylic carbons are double bonded, so they can't bond to 4 other atoms. Primary, sec, ter...are all reserved for sp3 carbons. In the case, an sp3 carbon bonding to 4 other carbons, it is called quarternary carbons

 

[Lunasly]

Thanks for the response. Hope im not annoying you with my questions. If something is sp3 hybridized, then it has 4 electron domains. However, if something is secondary and sp3 hybridized, then it must be bonded to two carbon based groups and a hydrogen atom in addition to the vinylic carbon it is bonded to. If this is the case, then the vinylic carbon doesn't count.

However, if I have a carbon bound to a vinylic carbon and an ethyl group or any R based group, isn't it only primary? For instance...

CH2 = CH -- CH2 -- Et

The two bolded carbons are the carbons of interest forming a single bond. The carbon that is also underlined is sp3 (4 electron domains), but is it considered primary or secondary?

 

[Chrisz]

Thanks for the response. Hope im not annoying you with my questions. If something is sp3 hybridized, then it has 4 electron domains. However, if something is secondary and sp3 hybridized, then it must be bonded to two carbon based groups and a hydrogen atom in addition to the vinylic carbon it is bonded to. If this is the case, then the vinylic carbon doesn't count.

However, if I have a carbon bound to a vinylic carbon and an ethyl group or any R based group, isn't it only primary? For instance...

CH2 = CH -- CH2 -- Et

The two bolded carbons are the carbons of interest forming a single bond. The carbon that is also underlined is sp3 (4 electron domains), but is it considered primary or secondary?

In this case, the underlined carbon is secondary carbon. This is exactly I been referring to in the earlier posts. After forming a bond with vinyllic carbon, the underlined propyl carbon becomes a secondary carbon because it is "now bonding to two other carbons." In case of ethyl, the ethyl also becomes a secondary because ethyl group is - c-c by itself. So after bonding to vinyllic carbon, it has two carbons bonded to it. In case of methyl group, it becomes primary after bonding to vinyllic

 

[Lunasly]

Ah ok. I was under the assumption that it was a methyl group bonded to the underlined carbon. In other words, I though the CH2 was always present and that we added a methyl or an ethyl group on to that.

Thanks for the help!