Defining an organic molecule

[RyanJ]

Hey there everyone!

 

I thought this may make an interesting debate, we had this debate today in chemistry and I would be very interested to hear your insights.

 

Organic chemistry is normally considered to be mainly involving compounds involving mainly carbon, hydrogen, oxygen, some sulphur, nitrogen, phosphorus and halogens too. In recent years this seems to have changed some what, we now have compounds that seem to break the traditional rules of what exactly defines an organic compound. Some compounds contain all sorts of things such as transition metals, alkali metals etc.

 

My question too you is this: How far does the distinction of an organic compound go in out current understanding of chemistry and what exactly do you think defines an organic compound today?

 

I'm hoping this will inspire some debate as it did in chemistry today, it was very interesting.

 

I'm still unsure how exactly to define an organic compound. Some of the molecules we have looked at certainly look like they are organic but their molecular formulas make me think again.

 

-- Ryan Jones

[5614]

In recent years this seems to have changed some what

I think that's recent years of your life, not in general. Grignard reagents (general formula: R-Mg-X where X is a halogen) have been around for about 100 years now. I found a little organometallic timeline here:

http://en.wikipedia.org/wiki/Organometallic_chemistry#Organometallic_chemistry_timeline

... so whilst there is currently a lot of work going into the field, it does have quite a bit of history behind it also.

 

Having other metals in organic compounds seems, I suppose, quite normal to me. Something like CH3-COONa for example, is a compound which just seems 'normal' to me, despite the alkali metal in it. Obviously you could argue that it's CH3COO- Na+, but the idea of a metal within an organic compound doesn't seem that strange to me.

 

Sticking in a transition metal makes you think again, just because it's a transition metal, but at the end of the day just like Cl, Na, Li or Mg can attach to the end of an organic compound, so can a transition metal.

 

I suppose I would define an organic compound as a compound containing carbon; except for CO2, CO & carbonates (and probably some others I haven't thought of).

[RyanJ]

Interesting comments as always 5614

 

I'd agree with you about the general statement (maybe a few other things like carbides added to your list?).

 

However there are compounds that still seem on the edge of what I would consider an organic compound like trimethylsilyl chloride, dimethylcopper lithium, tetrkis triphenylphosphine palladium. They all are clearly organic compounds on closer inspection but they really don't look like it from a molecular formula.

 

I'm glad you brought up organometallic compounds. These are really interesting substances. I would clearly consider them organic but they also seem like it when looked at from a general formula. (I'm actually fascinated by these, its a shame they aren't covered much in our chemistry modules though).

 

I'm just curious why you won't generalise carbonates and the like as organic? They fit your description of an organic compound because they do contain carbon. Even though I agree with you when you have to generalise that much the borders between organic and inorganic seem to have a merged definition.

 

Thanks for commenting 5614!

[YT2095]

if `R` is or can be used in a compound name, I would consider it generaly organic.

[woelen]

Something like CH3-COONa for example, is a compound which just seems 'normal' to me, despite the alkali metal in it. Obviously you could argue that it's CH3COO- Na+, but the idea of a metal within an organic compound doesn't seem that strange to me.

Such ionic compounds, as you mention here, are not special. There really is a big difference between such salts and real organometallic compounds. So, for me a compound like Ni(CH3COO)2 is not special, but a compound like Ni(C5H5)2 is special.

 

A good criterion for a compound being a real organometal compound is the presence of direct metal-C bonds. The latter type of compounds is quite new and extensive research on this kind of compounds only started in its full strength in the 1960's. Of course, some compounds of this type were known earlier,e.g. Ni(CO)4, but real understanding of this also was after WW II.

 

You now see a trend, where the term 'organic chemistry' is abandoned again. Nowadays there is the trend of simply speaking of 'carbon chemistry'. The border between classic organic and inorganic is not a sharp border, there is a large fuzzy area.

[RyanJ]

You now see a trend, where the term 'organic chemistry' is abandoned again. Nowadays there is the trend of simply speaking of 'carbon chemistry'. The border between classic organic and inorganic is not a sharp border, there is a large fuzzy area.

 

I think that's the point I'm trying to explore in the current context of the chemistry we understand, where are its borders? What actually defines the difference between an organic compound and an inorganic one? I'm hoping there would be some generalisation that could be used to decide but it seems not