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What type of intermolecular bonds are there between haloalkanes?

I understand the Halogen group would be partially negative, so there's a permanent dipole. I thought they were permanent dipole-induced dipole as the partially positive carbon is not exposed, but I read that they're permanent-permanent. Someone clear this up please!

Thank youu!

Reply 1

illusionz

20

The C-X bond has a permenant dipole. So there are going to be permenant dipole-dipole interactions. Unless it's a tertiary halogenoalkane then the carbon is suitably exposed for dipole interactions to have an effect.

Reply 2

TheBigI

The H atom would tend to be positive, so thats where the partially positive charge would come from for it to be permanent-permanent dipole :smile:

Reply 3

Basma

OP

Thanks you two. But at AS we're taught that the C-H bond is not polar, however I agree with you guys. Which reason would be right to give though? About the Carbon or the hydrogen?

Sorry for being slightly dim today!

Reply 4

EierVonSatan

21

Instantaneous dipole - induced dipole interactions (as always) but possibly some others, depending on the haloalkane.

Reply 5

illusionz

20

The H atom is not positive in a haloalkane. The delta charges are on the C and X (although if X=I then no charge).

Reply 6

TheBigI

According to my text book, if its H3C-CCl3 the right end would be negative, and the left positive then it is polar.

However, if it is CCl4, the Cl would be negative and the central C positive, this would mean it is non polar.

Reply 7

CaseySD

7

van der waals forces are the most important to remember when it comes to intermolecular forces between halgogenalkanes because it relates to other things such as boiling points of longer chains branched chains etc. although the bond being polar is also important

Reply 8

illusionz

20

TheBigI

According to my text book, if its H3C-CCl3 the right end would be negative, and the left positive then it is polar.

However, if it is CCl4, the Cl would be negative and the central C positive, this would mean it is non polar.

While that is true, you have to remember people may be talking about polar bonds rather than polar molecules.

Reply 9

Keckers

15

Van der Waals forces act on haloalkanes, the longer the molecules the higher the boiling point etc.

Also to consider are the polarity of the bonds between the carbon and the halogen (excluding iodine) which feature in nucleophilic substitution reactions

Reply 10

0201Bean

12

Basma

Thanks you two. But at AS we're taught that the C-H bond is not polar, however I agree with you guys. Which reason would be right to give though? About the Carbon or the hydrogen?

Sorry for being slightly dim today!

Van der Waals forces- Instantaneous-Induced dipoles.

I'm doing AS as well :biggrin:

Reply 11

presh5

9

it depends on the board u r doing what terminology you use for example i do ocr salters and they wont accept vander waals u have to be specific so for us it wud be permanent dipole - permanent dipole. If i wer u id take a look in ur text book n stuff to make sure u knw what terms they accept etc

Reply 12

Tomato_Soup1992

14

It would be van der waals and dipole-dipole surely...

Reply 13

Moe Lester

15

EierVonSatan

Instantaneous dipole - induced dipole interactions (as always) but possibly some others, depending on the haloalkane.

Is there a cut off regards it forming a C-Halogen perm. dipole then? :p:

Reply 14

najeezy

12

basically, first of all, all molecules have instantaneous dipole - induced dipole, a halogeno alkane will have a permanent dipole - permanent dipole because the halogen is more electronegative than the hydrocarbon chain, this is the only part of the molecule that has a pd-pd, which is C-X (X= Halogen), C and H have a very small difference in electronegativity so it is negligible and not taken into account, permanent dipole - induced dipole doesnt come up in AS/A2, at least not in my board, so its basically just a mixture of ID-ID and PD-PD. Hope that clears something up.

Reply 15

EierVonSatan

21

Moe Lester

Is there a cut off regards it forming a C-Halogen perm. dipole then? :p:

Well, C-I bonds are essentially non-polar plus if you have molecules like carbon tetrafluoride it will have no overall dipole despite the very polar C-F bonds.

Reply 16

Moe Lester

15

EierVonSatan

Well, C-I bonds are essentially non-polar plus if you have molecules like carbon tetrafluoride it will have no overall dipole despite the very polar C-F bonds.

Thanks

So Iodine is due to electronegativity I assume - electron shielding in this case?

Oh I see, because the flourine is in all directions - thus cancelling out any polarity?

Reply 17

EierVonSatan

21

Moe Lester

Thanks

So Iodine is due to electronegativity I assume - electron shielding in this case?

Yeah, more shells shielding the nucleus.

Oh I see, because the flourine is in all directions - thus cancelling out any polarity?

Indeedy

Reply 18

Moe Lester

15

EierVonSatan

Yeah, more shells shielding the nucleus.

Indeedy :smile:

Thanks

Reply 19

Kyle_S-C

12

EierVonSatan

Well, C-I bonds are essentially non-polar plus if you have molecules like carbon tetrafluoride it will have no overall dipole despite the very polar C-F bonds.

What about the ever so important

\text{C}-\text{H}\cdots\text{X}

halogen bonds? :p:

I swear some of our courses make stuff up...

What type of intermolecular bonds are there between haloalkanes?

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