Organic Chemistry

[letaps]

Hey,

What are the meta, ortha, para deactivating and activating groups?

and

Is there an easy way to remember the groups?

Thanks

---

Members don't see this ad.

 

[MILK07]

Ortho-Para directing groupselectron donating because of the lone pairs on the oxygen or nitrogen groups)

-NH2
-NHR
-NR2
-OH
-OR
-NHCOR
-OCOR
-R
-benzene

Meta directing (electron withdrawing because of the partial positive charge on the carbons in the carbonyl group or the C-N bond; also the positive charge in NH3 and the electronegative differences in the CF3 and CCl3 bonds, again making carbon partially positive.)

-COH
-COOH
-COOR
-CONH2
-CN
-NO2
-NH3+
-CF3
-CCl3

Exception: Halogens (F, Br, Cl, and I) are electron withdrawing but are ortho-para directors

Good luck and let me know if you have any more questions.

 

[ballofnerves]

One general rule is that if the atom bonded to the benzene ring has lone pairs, it is activating, since it could donate electron density to the ring, making the benzene ring more reactive. Examples of these groups are the methoxy group -OMe, hydroxyl group -OH, amino group -NH2, etc. These groups will promote ortho/para substitution

Additionally, alkyl groups (e.g., methyl, ethyl, etc.) and phenyl groups donate electron density even though there are no lone pairs on the atom bonded to the ring. Since they donate electron density, they are activating and will promote ortho/para substitution.

It is slightly trickier with halogens. Because halogens (e.g., -Cl, -Br, -F) are very, very electronegative, if they are bonded to a ring, they will withdraw electron density, so they are deactivators. However, they still have lone pairs, so they will promote ortho/para substitution.

Meta deactivators do not have lone pairs on the atom attached to the benzene ring. Examples of these groups are the nitro group -NO2, and generally, carbonyl groups such as -COH or -COMe. This is because the carbonyl carbon is electron-deprived, so it desperately wants to withdraw electron density from the ring, which would make the benzene less reactive.

So to sum up: if the atom bonded to the ring has lone pairs, it is a ortho/para activator. The exceptions are halogens (which are ortho/para deactivators) and alkyl groups (which don't have lone pairs but are still ortho/para activators.)

If the atom bonded to the ring has no lone pairs, it is a meta deactivator. Of course, the exception to this rule are the aforementioned alkyl groups.

 

[CdanceNS]

Another thing that is easy to remember is that a singly bonded oxygen is electron donating (activating) and a doubly bonded oxygen is withdrawing (deactivating). A nitrogen with 3 bonds is electron donating (activating) and a nitrogen with 4 bonds is electron withdrawing (deactivating). Those 2 rules let you figure out a whole lot of functional groups easily, without memorizing long lists.

 

[cornpops21]

There's basically 2 rules and an exception:

1) Any carbonyl-containing functional group will be electron-withdrawing and meta-directing. (NO2 groups will also fall under this group b/c of the doubly-bonded N)

2) Anything with a lone pair will be electron-donating and ortho-para directing. (alkyl groups will donate)

3) Halogens are electron-withdrawing (b/c of electronegativity) but have the lone pair, allowing them to be ortho-para directors.

These are really general rules that should get you through any benzene substitution problem.

 

[wrathofgod64]

Hmm, according to EK the AAMC announced they wont ask questions on benzene starting in 2003. Is it still possible to see ortho/para/meta questions?

 

[inaccensa]

Ortho-Para directing groupselectron donating because of the lone pairs on the oxygen or nitrogen groups)

-NH2
-NHR
-NR2
-OH
-OR
-NHCOR
-OCOR
-R
-benzene

Meta directing (electron withdrawing because of the partial positive charge on the carbons in the carbonyl group or the C-N bond; also the positive charge in NH3 and the electronegative differences in the CF3 and CCl3 bonds, again making carbon partially positive.)

-COH
-COOH
-COOR
-CONH2
-CN
-NO2
-NH3+
-CF3
-CCl3

Exception: Halogens (F, Br, Cl, and I) are electron withdrawing but are ortho-para directors

Good luck and let me know if you have any more questions.

Can anyone please explain how the bonding of OCOR is different from COOR with an example