dipole moment
John Doe III
Is this a correct polarity order?
Most polar--------------------least polar
CH3Cl > CHCl3 > CHCl2 > CH4
Attila the Bum
What do you mean by "polarity:?
Atty (... most north polarity, or
most south polarity?)
John Doe III
>
Jona
Hash: SHA1
I think he's talking about the polarisation of the C-H bond.
Are you sure you don't mean "CH2Cl2" instead of "CHCl2"?
It should be CHCl3 ">" CH2Cl2 ">" CH3Cl ">" CH4
Chlorine atoms attract electrons due to their electronegativity.
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John Doe III
> Are you sure you don't mean "CH2Cl2" instead of "CHCl2"?
I meant CH2Cl2
> It should be CHCl3 ">" CH2Cl2 ">" CH3Cl ">" CH4
> Chlorine atoms attract electrons due to their electronegativity.
WRONG ANSWER (based on my book)
Bob
That's cuz Jona changed (or re-interpreted) the question.
Data, from CRC Handbook:
dipole moment, in debyes
CHCl3: 1.01
CH2Cl2: 1.60
CH3Cl: 1.87
Same trend holds for Br. But not for F:
CHF3: 1.65
CH2F2: 1.97
CH3F: 1.85
bob
John Doe III
>
> dipole moment, in debyes
>
> CHCl3: 1.01
> CH2Cl2: 1.60
> CH3Cl: 1.87
>
> Same trend holds for Br. But not for F:
>
> CHF3: 1.65
> CH2F2: 1.97
> CH3F: 1.85
>
rek...@gmail.com
Dipole moment is essentially proportional to a gradient of electron
density (units of C.m or debyes). As you probably know, CH3 is
electron donating and Cl is electron withdrawing. Having only one Cl
and a heavily electron-donating methyl carbon creates a larger gradient
than having 3 Cl's trying to pull on a carbon with only one H, which is
less electron-donating.
John Doe III
> Dipole moment is essentially proportional to a gradient of electron
> density (units of C.m or debyes). As you probably know, CH3 is
> electron donating and Cl is electron withdrawing. Having only one Cl
> and a heavily electron-donating methyl carbon creates a larger gradient
> than having 3 Cl's trying to pull on a carbon with only one H, which is
> less electron-donating.
>
There is only one carbon, which methyl group are you talking about?
rek...@gmail.com
It was a redundant statement. The only carbon there, which is also a
methyl carbon.
Bob
Agreed.
Let's assume for now that the data I posted is correct. (You might
want to verify from another source. CRC is not immune to errors. And I
am not immune to typos, though I think I got these correct.)
The problem is that dipole moment depends on charge differences but
also on distances. So the simple idea that more of a very EN atom
means greater dipole moment ignores the possible effect of subtle
differences in molecular geometry.
If you really want to pursue this, look up known (not nominal) atomic
coordinates, and see what the shapes are. Remember that they may be
quite different for the Cl and F cpds, as F is much smaller.
Editorial comment... This is not something I would worry about much.
It is one thing to generally distinguish polar and nonpolar compounds.
But predicting the subtle effects here seems unnecessary, for most
people. If one has need of these numbers, one can look them up.
bob
James Copeland
obtained from the most recent Lange's Handbook of Chemistry. You can see
that they are nearly the same as those given by CRC. (Certainly the ordering
is the same.)
CHCl3: 1.04
CH2Cl2: 1.6
CH3Cl: 1.892
Jim C.
"Bob" <bbx...@excite.com.XXXX> wrote in message
news:ufvff1tv4osujvs19...@4ax.com...
Bob
wrote:
>Your CRC data are most likely reasonably correct. Here are the values
>obtained from the most recent Lange's Handbook of Chemistry. You can see
>that they are nearly the same as those given by CRC. (Certainly the ordering
>is the same.)
>CHCl3: 1.04
>CH2Cl2: 1.6
>CH3Cl: 1.892
thanks, Jim.
Can you confirm the data (or at least the trend) for the F cpds? I
think part of the concern is that the trends seem to be different for
Cl,Br vs F.
bob
James Copeland
Handbook of Chemistry, 15th ed., 1999)
CHF3: 1.651 (CHCl3: 1.04)
CH2F2: 1.978 (CH2Cl2: 1.6)
CH3F: 1.858 (CH3Cl: 1.892)
So we can see that in both cases the trihalogenated methane is smallest
within a series, but the mono- and dihalogenated methanes are reversed in
order of dipole moments (CH2Cl2 < CH3Cl, but CH2F2 > CH3F). No, right off
hand I have no explanation of why.
Jim C.
"Bob" <bbx...@excite.com.XXXX> wrote in message
news:li8gf1hdr094kuj6e...@4ax.com...
Attila the Bum
James Copeland wrote:
> Yes. Here are the data for the fluoridated methanes (same source: Lange's
> Handbook of Chemistry, 15th ed., 1999)
>
> CHF3: 1.651 (CHCl3: 1.04)
> CH2F2: 1.978 (CH2Cl2: 1.6)
> CH3F: 1.858 (CH3Cl: 1.892)
>
> So we can see that in both cases the trihalogenated methane is smallest
> within a series, but the mono- and dihalogenated methanes are reversed in
> order of dipole moments (CH2Cl2 < CH3Cl, but CH2F2 > CH3F). No, right off
> hand I have no explanation of why.
> Jim C.
Probably different Coulombic
environments. Fluorine is
"small and hard"; Chlorine
is "large and mushy". A symmetry
argument would support the high
value for CH2F2; bulk, for CHCl3
I'd bet Br and I analogues
would show the same trends
as Cl. But what do I know,
I only have an education in
chemistry, not nuclear
physics :-)
Atty (... sorta funny, how those
more dense, float. More
beverage, anyone?)
James Copeland
CH3Br: 1.82
CH2Br2: 1.43
CHBr3: 0.99
CH3I: 1.62
CH2I2: 1.08
CHI3: 0.90
> CHF3: 1.651 (CHCl3: 1.04)
> CH2F2: 1.978 (CH2Cl2: 1.6)
> CH3F: 1.858 (CH3Cl: 1.892)
>
> So apparently only the fluoridated series is out of order compared to the
> other three.
> I have no explanation of why. (Sorry; I can't find data for astatine
> methanes ;-)
Attila the Bum
James Copeland wrote:
> Okay. Here's the whole ball of wax for the halogenated methanes.
X= F Cl Br I
CH3X 1.858 1.893 1.82 1.62
CH2X2 1.978 1.6 1.43 1.08
CHX3 1.651 1.04 0.99 0.90
Lange's 15th Edition also shows 1.08 for
the diiodo compound.
Don't I recall something about N, O, and F,
having the ability to form hydrogen bonds?
And aren't dipole moments measured in what
is essentially a capacitance cell, where the
drag on the applied A.C. is proportional to
the dipole moment of the substance being
tested?
Atty