How do molecules smell?

[Physia]

I need help finding how molecules make an ester smell good after a condensation reaction.

 

Can anybody help? Thank you in advance.

[imp]

I need help finding how molecules make an ester smell good after a condensation reaction.

 

Can anybody help? Thank you in advance.

 

Esters generally have pleasant perceived odors, true. To explain the physiological process by which humans distinguish between "good" and "bad" smells might be outside the scope of a simple science thread; it is certainly beyond my ability, sorry. Still, we should be aware that cultural differences determine to an extent what may be an acceptable smell to some, while it is disagreeable to others.

 

For example, some like the smell of gasoline; many do not. Sorry to not be of more help. imp

[Physia]

Esters generally have pleasant perceived odors, true. To explain the physiological process by which humans distinguish between "good" and "bad" smells might be outside the scope of a simple science thread; it is certainly beyond my ability, sorry. Still, we should be aware that cultural differences determine to an extent what may be an acceptable smell to some, while it is disagreeable to others.

 

For example, some like the smell of gasoline; many do not. Sorry to not be of more help. imp

 

It's fine. I researched about it and couldn't find any information. Maybe I wasn't typing in the correct words in the search engine, who knows.

 

However, my AP Chemistry teacher have told me that there is something that makes a certain substance (alcohol for example) smell the way it does. Are you able to identify that substance?

 

 

P.S. nice forum, hope I know about his before now.

[fredrik]

Sensations are complex and have several components.

 

The primary transducer is an olfactory receptor neurons, which from what I recall contains transmembrane proteins that bind to special molecules. The binding changes the proteins and via a series of reactions in the end causes the neuron to create an electric signal that is sent to the brain via the olfactory nerve. Here there olfactory receptor proteins clearly have different affinities to bind to different odour molecules, in general these affinities are probably also regulated in response to several other things. This is the case also with taste receptors. So on the transducer side there are a complex regulatory network that regulates what molecules or functional groups that tend to bind to the receptors.

 

Second question, and probably even more complicated, is what happens to the electric nerve signal in the brain. The brain have to "decode" and interpret the electrical signals from specific neurons in context. Meaning the preception of a single molecule may vary with the general context, both ambient, and the rest of the body, and in comparasion with memory associations you have had with this signal before.

 

So there two parts, the mechanism how a molecule generates a electric nerve signal to the brain. And how the brain interprets/handles this signal in context.

 

Both parts are complex and there is not yet complete knowledge of how this all works in detail. The first part, one can study, then one usually identifies a specific receptor proteins, and the gene that encodes it. Then one can study the regulation of this gene, as well as the regulations of the protein itself.

 

I haven't look much into smell, but I did some reading on salt and sweet receptors and how they respond differently to various ions, but the conclusion is that it's complex, and ontop of that you have the brain treatise which I think there is even less knowlegdge of.

 

/Fredrik

[carol]

different smells and tastes are interpreted by triggering certain combinations of receptors. so, i guess different chemicals trigger different types of receptors.

[Physia]

Seeing you guys' replies, I just thought I would share with you the alcohols and organic acids that I will be using in my Synthesis Ester Lab, and you guys can give me an analysis on which you think will smell better:

 

Acids

Formic acid (HCOOH)

Acetic acid (CH3COOH)

Propionic acid (C3H6O2)

Butyric acid (C4H8O2)

Salicylic acid [C6H4(OH)COOH]

Anthranilic acid (NH2C6H4COOH]

 

Alcohols

Methanol (CH3OH)

Ethanol (C2H5OH)

1-octanol [CH3(CH2)7OH]

2-methyl-1-butanol [CH3CH2C(CH32)OH]

Isobutanol (C3H10O)

1-propanol (C3H8O)

Isoamyl alcohol [(CH3)2CH(CH2)2OH]

Benzyl alcohol (C6H5CH2OH)

 

Numbers are all subnumbers, you guys know that right?

Okay anyways, I have a total of 48 reactions. Each alcohol will be mixed with all of the acids.

 

If you guys can, could you give me an idea of which reaction will smell better and a reason for that? Thank you in advance, I appreciate it.

[fredrik]

If you guys can, could you give me an idea of which reaction will smell better and a reason for that? Thank you in advance, I appreciate it.

 

The question of which smells "better" is obviously a subjective one. Two people will in general disagree on which smells better, depending on associations and other things. Or past experience that certain smells associate with stale food, fresh fruit etc. So smell is a tool to get good food and avoid bad good. What's best is bound to be subjective in any case.

 

So I'm not sure what you're asking?

 

/Fredrik

[fredrik]

For example, what smells "better", banana or pear? And do you prove it?

 

/Fredrik

[Genecks]

Molecules smell like keys.

 

For example, what smells "better", banana or pear? And do you prove it?

 

/Fredrik

 

I suppose it would be possible to prove, but you'd have to fight against the bio-social-psycho triangle. It could be argued, but that is not the point of this thread. Now in the sense of this thread, I suppose the person is questioning different types of stimulation (sweet, bitter, etc.) of the brain and its receptors.

[Physia]

Molecules smell like keys.

 

 

 

I suppose it would be possible to prove, but you'd have to fight against the bio-social-psycho triangle. It could be argued, but that is not the point of this thread. Now in the sense of this thread, I suppose the person is questioning different types of stimulation (sweet, bitter, etc.) of the brain and its receptors.

 

Close enough.

 

Let me try to explain one more time.

I am trying to identify the molecules that causes the smells in the produced esters, and thus figuring out which one smells better. I'm trying to do that before even doing the experiment though.

[Genecks]

Perhaps some chemical reactions with the esters occur within the atmosphere, thus turning them into acids/bases/other, of which the are the molecules that act as keys for the receptors.

 

You're not simply talking about the esters but the molecules that can come from the esters which might cause a pleasant or non-pleasant smell, right?

 

Organic chemists are often taught to identify certain functional groups in an organic

compound by its smell while analyzing organic compounds. A fruity smell is commonly

associated with an ester, the smell of bitter almonds with ketones and that of rotten eggs with

compounds having -SH functional group. This has led to a theory that the smell of a chemical

depends on properties such as the shape, chemical structure or electrical charge of its

molecules. According to this theory, molecules with different shapes/structures dock at

different receptors in the nose (our nose contain several million receptors--of 500 to 1000

different types). But recently some scientists have identified compounds which are structurally

totally unrelated but still have similar odours. For example, decaborane smells of rotten eggs

although it has no -SH functional group. This has led to the suggestion that it is the presence of

certain vibrational bands in the infra red spectrum of the substance that may stimulate a

particular odour. An S-H bond vibrates at about 2500 wave numbers ( wave number =

1/wavelength) so does a B-H bond found in boranes. But there are controversies still and

scientists cannot design compounds which may definitely give off a particular odor. We cannot

therefore make transducers to reproduce all smells -- like a loudspeaker for sounds or a cathode

ray tube for images. Smell, therefore, cannot be transmitted like sound or light signals over

very large distances.

 

http://www.scribd.com/word/download/35336?extension=pdf

 

Here's something else: http://notes.chem.usyd.edu.au/course/schmidtt/chem1101/lectures/lecture%201101_17_2007.pdf

[fredrik]

Close enough.

 

Let me try to explain one more time.

I am trying to identify the molecules that causes the smells in the produced esters, and thus figuring out which one smells better. I'm trying to do that before even doing the experiment though.

 

It's still unclear to me how you define "better smelling". I can imagine two ways, either the subjective question what do You think smells better, and then interpret freely. Or to consider the biological value of finding food with a certain smell (good, healthy food), that may somehow define some prior preferences to flavours. Maybe the traits to o recognizing good food and dangerous food is preserved and there is some positive feedback to the brain upon smelling something "good". But how to calculate and quantify that seems very difficult, and probably still fuzzy since there may be individual to individual variation anyway.

 

If I were you, I'd start doing some reaserch on the genes, and try to find papers on each sensor type.

 

Here is one paper

"The human olfactory receptor gene family"

http://www.pnas.org/cgi/reprint/101/8/2584.pdf

 

I'm not sure about humans, but for other organisms one can find genome detabases and links to papers related to certain genes.

 

About practical parts of other things, esters you make in the lab typically appear in some solution in equilibrium with the acid and alcohols so there would possibly be undertones of the respective acids and alcohols in a real test. And ester reaction has different equilibrium points, and various flavour odour tresholds.

 

I'm not sure it's interesting but I wrote some notes on this in the home brew digest (hbd.org) some time ago in the context of beer aging, where there is a balance between esters, alcohol and carboxylic acid and their tresholds and wether the aging improves or worsens the flavour. Generally the ester smells good and the carboxylic does not. Some acids have fairly low tresholds too. Some people argued that harsh higher alcohols mellow since then esterified, but thermodynamic reasoning shows that this is usually unfavourable. The more likely candidate for harshness might have been acids which have low tresholds and relatively speaking more reduced during aging in some cases. hbd seems temporary down so I can't supply the link. But search for "Thermodynamics of Esterifiction" and you may find some exmnples.

 

/Fredrik

[Genecks]

I suppose better smelling refers to most pleasurable. In the sense of pleasure, there are neurotransmitters and chemicals involved. Therefore, I suspect a change, for which would lead to an increase in pleasure, in those would conclude a "better smelling" substance. If not, then an association to taste and experience with smell with change in neurochemistry could help determine pleasurable smells.

 

 

I'm thinking an axiological view isn't too well suited, but perhaps a more physicalist approach would do.

 

Anyway, let us try to maintain with the discussion of original topic.

[fredrik]

I suppose better smelling refers to most pleasurable. In the sense of pleasure, there are neurotransmitters and chemicals involved. Therefore, I suspect a change, for which would lead to an increase in pleasure, in those would conclude a "better smelling" substance. If not, then an association to taste and experience with smell with change in neurochemistry could help determine pleasurable smells.

 

Ok, that makes sense, that some smells gives positive feedback to the brain. But that seems complex And wouldn't this possibly be slightly dependent on individual too, and your genes, rendering the answer subjective to the individual? I'm not sure how much research there is on that. Anyway, I got the impression that the original question was in relation to some more basic estersynthesis chemistry lab? Maybe I didn't get the question posed in the proper context?

 

When I looked into taste bud receptors some time ago I was surprised to see how little research that has been done. Part of the problem is that it's not easy to hijack - in vivo - the nerve lines in humans... for obvious reasons. So much research is made on rats and mice. And some test panel testing on humans. But in the end the biochemical and neurochemical knowledge of something as "simple" as sweetness and salt receptors is incomplete even though the basic mechanism are often more or less known. Also, research is often made with single compounds... like a particular salt or so. But not so much is known what the response is to other compounds.

 

/Fredrik

[Physia]

I think you guys went a little bit off-topic.

 

Fredrik got it right, it's about a basic synthesis chemistry lab.

 

Thank you very much for the links and information.

[DrDNA]

I realize that this was posted months but I just saw it...

Actually, I think that you guys may be trying to make it more difficult than it really is. Esterification generally makes a molecule more volatile compared to it's charged (acidic) counterpart. Therefore, esters are more likely to be detected by receptors in the olfactory system. Perhaps this is what was meant by "smell better" = better or easier to smell?

[greysteel_M6]

ester = fruity smell

 

/\ are you serious? No we're in Iraq because we went in there to remove dangerous weapons from a dangerous regime, that prime objective failed and it has turned into some gd post-facto humanitarian mission.

[Physia]

ester = fruity smell

 

/\ are you serious? No we're in Iraq because we went in there to remove dangerous weapons from a dangerous regime, that prime objective failed and it has turned into some gd post-facto humanitarian mission.

 

I'm a bit late, but I speak from an intellectual point of view regarding the long-term dangerousness of this regime; which in turn is spreading every day. Take France for example, and see for yourself.

[iNow]

I'm a bit late, but I speak from an intellectual point of view regarding the long-term dangerousness of this regime; which in turn is spreading every day. Take France for example, and see for yourself.

 

Surely you must mean the Bush regime. Also, why hate France? They have universal health care, eat fatty foods, drink great wine, have wonderful romance, and smoke, yet still manage to live longer than those in the US.

 

Hating others fixes zero problems. Remove cranium from colon and try again.

[Physia]

Surely you must mean the Bush regime. Also, why hate France? They have universal health care, eat fatty foods, drink great wine, have wonderful romance, and smoke, yet still manage to live longer than those in the US.

 

Hating others fixes zero problems. Remove cranium from colon and try again.

 

Who said I hate France anywhere? In fact, I applaud Sarkozy's positions and the improved way of thinking of a western president regarding the east, with all its social and political attributes.

 

By hinting France in my former post, I was trying to lead the person into the rapid uncontrolled expansion of Islam and radical Islam around Europe, particularly in France.

In 20 years, France's majority will be composed of Muslims and the minority of everything else. That's my only hint.

[iNow]

That's my only hint.

 

Thanks for the clarification. I live in Texas, where any reference to "France" tends most often to be delivered with deragotory intent.

[DrDNA]

Thanks for the clarification. I live in Texas, where any reference to "France" tends most often to be delivered with deragotory intent.

 

Damn french fries........