Dipole moment?

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I'm reading in my organic chemistry text about the structure of alkyl halides, as a background to why certain reactions happen (specifically radical halogenation). In it there's a table of halomethanes, that tells the bond length, bond strength, and dipole moment. It pretty much looks like this:

Fluoromethane Bond length 136pm, Bond strength 108 kcal/mol, Dipole moment (D) 1.85
Bromomethane Bond length 178pm, Bond strength 84 kcal/mol, Dipole moment (D) 1.87
Chloromethane Bond length 193pm, Bond strength 70 kcal/mol, Dipole moment (D) 1.81
Iodomethane Bond length 214pm, Bond strength 56 kcal/mol, Dipole moment (D) 1.62

I understand what's going on with the dipole moment, but exactly what does it mean to have a Dipole moment of 1.85? Also, can these numbers be calculated to compared each other?

If you're curious, this is from the text "Organic Chemistry, 7th Edition, McMurry", page 335. And this is NOT a homework assignment, just a concept question. =)
 

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chemisttree
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I'm reading in my organic chemistry text about the structure of alkyl halides, as a background to why certain reactions happen (specifically radical halogenation). In it there's a table of halomethanes, that tells the bond length, bond strength, and dipole moment. It pretty much looks like this:

Fluoromethane Bond length 136pm, Bond strength 108 kcal/mol, Dipole moment (D) 1.85
Bromomethane Bond length 178pm, Bond strength 84 kcal/mol, Dipole moment (D) 1.87
Chloromethane Bond length 193pm, Bond strength 70 kcal/mol, Dipole moment (D) 1.81
Iodomethane Bond length 214pm, Bond strength 56 kcal/mol, Dipole moment (D) 1.62

I understand what's going on with the dipole moment, but exactly what does it mean to have a Dipole moment of 1.85? Also, can these numbers be calculated to compared each other?

If you're curious, this is from the text "Organic Chemistry, 7th Edition, McMurry", page 335. And this is NOT a homework assignment, just a concept question. =)
The 1.85 is expressed in Debye's (D). Good Google term. Measurement is... challenging. The numbers are measured. I'm not sure if you can calculate it accurately but you may be able to calculate a relative ranking.
 

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