Halogens direct Ortho/Para??

[UCSD1984]

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They are deactivating, yet the explanation to #212 in Destroyer (Page 59) states that even though they are deactivating, they direct Ortho/Para. I don't recall Chad saying this, ever. It's also not how it's stated on his chapter outlines.

 

[DrRoyal Pains]

Yea, its in there. Although they are deactivating, one would think they direct meta, but they do in fact direct O/P. Check out his downloadable sheet for that section. It's got a nice chart.

 

[jwnichols21]

They are deactivating, yet the explanation to #212 in Destroyer (Page 59) states that even though they are deactivating, they direct Ortho/Para. I don't recall Chad saying this, ever. It's also not how it's stated on his chapter outlines.

Yup, this is from Chad's notes. Halogens are the exception-they are grouped in with the Electron Donating substituents and direct Ortho/Para.

 

[UCSD1984]

Mmmm, I was looking at that table way wrong. I learned something new and important. Thanks fellas.

 

[Demps]

Just one more thing to the halogen being deactivating and ortho/para directing to the benzene:

It still makes the benzene acidic.

 

[UCSD1984]

Just one more thing to the halogen being deactivating and ortho/para directing to the benzene:

It still makes the benzene acidic.

And still makes Benzene reactions slower?

 

[Demps]

And still makes Benzene reactions slower?

you mean relative to a regular benzene ring right? like chlorobenzene vs. benzene

Benzene reacts better/faster than chlorobenzene

 

[jefff]

Yup, this is from Chad's notes. Halogens are the exception-they are grouped in with the Electron Donating substituents and direct Ortho/Para.

Just one more thing to the halogen being deactivating and ortho/para directing to the benzene:

It still makes the benzene acidic.

I'm pretty sure they are grouped with electron withdrawers (although weakly) (but direct o/p), and for this reason, as demps mentioned, they are deactivating and increase acidity

the way i do it, instead on memorizing any specific table is as follows:

--electron withdrawers: have a bond directly on the benzene ring (example1: -COOH) with an element that assumes a delta +, a more electron negative element (in this example Oxygen) is attached on the opposite side and so like i mentioned the Carbon receives a delta + while the Oxygen holds a delta -

-----HALOGENS (example2) are special because they are, on the periodic table, right next to noble gases and would LOVE an extra electron to have 8 in their valance shell therefore weakly withdrawing

--electron donors: have a bond directly on the benzene ring (example3: -OCH3) with an element that holds a delta - which in this case is Oxygen, the Carbon receives a delta +

**directing: I count in multiples of 2 starting with the first element attached to most electronegative (but closest to the ring as possible--or like you'll see the ortho/para directors the first carbon is directly on the ring)

*****example 1: i start with start counting with the Carbon (1) (double bonded to the Oxygen), Carbon (2) (first one on the ring)
---- obviously cant direct here
---- again count in multiples of 2
---- now ortho carbon (1), meta carbon (2)
---------so example 1 we established was electron withdrawing and since the carbon we landed on @ the second count of 2 was meta...its a meta director


*****example 3: i start with start counting with the Carbon (1) (directly on the ring), Carbon (2) (ortho)
---- we CAN direct here! (so right off the bat we should know that we'll be directing o/p)
----but incase you dont see it or dont want to assume anything..
---- again count in multiples of 2
---- now meta carbon (1), para carbon (2)
---- we CAN direct here!
---------so example 3 we established was electron donor and since the carbon we landed on @ the first count of 2 was ortho, and at the second count of 2 was para...its an o/p director

example 2 is the same as example 3 in regards to the counting:
*****example 2: i start with start counting with the Carbon (1) (directly on the ring), Carbon (2) (ortho)
---- we CAN direct here! (so right off the bat we should know that we'll be directing o/p)
----but incase you dont see it or dont want to assume anything..
---- again count in multiples of 2
---- now meta carbon (1), para carbon (2)
---- we CAN direct here!
---------so example 2 we established it was weakly electron withdrawing (since its special as a halogen and it wants to be like a noble gas so bad)... and since the carbon we landed on @ the first count of 2 was ortho, and at the second count of 2 was para...its an o/p director


remember benzene is stable due to its conjugation within the pi system -- it is very electron rich throughout the ring and benzene likes it that way, any bond to it will "make it less reactive"...especially if the bond was made to an element that was electron withdrawing.......but if bond is directly to an element that is electron donating then it is considered to be "activating" this term is best thought of as a reference like...its more activating/active than it would be if an electron withdrawer was attached to the ring, but still its most active when nothing is bound

also recall acids ACCEPT E-s (lewis definition) -- so if you have an electron withdrawing group attached to a ring then you have greater delocalization of electrons (can be thought of as electron density being pulled/resonating out of the ring).....so if electrons are delocalized out of the ring then the ring would love to ACCEPT E-s therefore become more acidic

sorry for the wall of text and lack of appropriate punctuation

 

[UCSD1984]

I'm pretty sure they are grouped with electron withdrawers (although weakly) (but direct o/p), and for this reason, as demps mentioned, they are deactivating and increase acidity

the way i do it, instead on memorizing any specific table is as follows:

--electron withdrawers: have a bond directly on the benzene ring (example1: -COOH) with an element that assumes a delta +, a more electron negative element (in this example Oxygen) is attached on the opposite side and so like i mentioned the Carbon receives a delta + while the Oxygen holds a delta -

-----HALOGENS (example2) are special because they are, on the periodic table, right next to noble gases and would LOVE an extra electron to have 8 in their valance shell therefore weakly withdrawing

--electron donors: have a bond directly on the benzene ring (example3: -OCH3) with an element that holds a delta - which in this case is Oxygen, the Carbon receives a delta +

**directing: I count in multiples of 2 starting with the first element attached to most electronegative (but closest to the ring as possible--or like you'll see the ortho/para directors the first carbon is directly on the ring)

*****example 1: i start with start counting with the Carbon (1) (double bonded to the Oxygen), Carbon (2) (first one on the ring)
---- obviously cant direct here
---- again count in multiples of 2
---- now ortho carbon (1), meta carbon (2)
---------so example 1 we established was electron withdrawing and since the carbon we landed on @ the second count of 2 was meta...its a meta director


*****example 3: i start with start counting with the Carbon (1) (directly on the ring), Carbon (2) (ortho)
---- we CAN direct here! (so right off the bat we should know that we'll be directing o/p)
----but incase you dont see it or dont want to assume anything..
---- again count in multiples of 2
---- now meta carbon (1), para carbon (2)
---- we CAN direct here!
---------so example 3 we established was electron donor and since the carbon we landed on @ the first count of 2 was ortho, and at the second count of 2 was para...its an o/p director

example 2 is the same as example 3 in regards to the counting:
*****example 2: i start with start counting with the Carbon (1) (directly on the ring), Carbon (2) (ortho)
---- we CAN direct here! (so right off the bat we should know that we'll be directing o/p)
----but incase you dont see it or dont want to assume anything..
---- again count in multiples of 2
---- now meta carbon (1), para carbon (2)
---- we CAN direct here!
---------so example 2 we established it was weakly electron withdrawing (since its special as a halogen and it wants to be like a noble gas so bad)... and since the carbon we landed on @ the first count of 2 was ortho, and at the second count of 2 was para...its an o/p director


remember benzene is stable due to its conjugation within the pi system -- it is very electron rich throughout the ring and benzene likes it that way, any bond to it will "make it less reactive"...especially if the bond was made to an element that was electron withdrawing.......but if bond is directly to an element that is electron donating then it is considered to be "activating" this term is best thought of as a reference like...its more activating/active than it would be if an electron withdrawer was attached to the ring, but still its most active when nothing is bound

also recall acids ACCEPT E-s (lewis definition) -- so if you have an electron withdrawing group attached to a ring then you have greater delocalization of electrons (can be thought of as electron density being pulled/resonating out of the ring).....so if electrons are delocalized out of the ring then the ring would love to ACCEPT E-s therefore become more acidic

sorry for the wall of text and lack of appropriate punctuation

I really like this breakdown, I appreciate it. I copy and pasted it for reference later in case I need to review. Fantastic explanations, thanks my friend.

 

[loganheinrich]

I use very similar thinking to Jefff's post except that on the electron donors, the atom bonded directly to the benzene ring usually has an unpaired electron pair or two that it can then donate. The other activating/OP directors are R groups (E.G. a methyl group) and we know that, even without unpaired electrons, these groups are donating.

 

[jefff]

I really like this breakdown, I appreciate it. I copy and pasted it for reference later in case I need to review. Fantastic explanations, thanks my friend.

glad i could help 🙂

I use very similar thinking to Jefff's post except that on the electron donors, the atom bonded directly to the benzene ring usually has an unpaired electron pair or two that it can then donate. The other activating/OP directors are R groups (E.G. a methyl group) and we know that, even without unpaired electrons, these groups are donating.

ah yes, good call 👍...forgot to add that
they donate via induction through their sigma bond