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Carboxylic acid nomenclature and properties

Video transcript

let's look at the nomenclature and physical properties of carboxylic acids and we'll start with nomenclature so if we wanted to name this carboxylic acid it's the simplest one possible there's one carbon so a one carbon carboxylic acid if we had a one carbon alkane we would call that methane to name a carboxylic acid you dropped the e ending and add acid and so this one would be methanoic acid so let me go ahead and write this out so methanoic acid you can see we've dropped the e and added oeq and then acid methanoic acid is the i u-pack name for this molecule the common name for this is formic acid which is what you'll hear more often so formic acid and the name comes from the Latin word for aunt because formic acid is found in antvenom and there are lots of really cool carboxylic acids with interesting common names such as such as this example here alright let's look at this one so a two carbon carboxylic acid so using IU Pack nomenclature that would be ethanoic acid alright so it'd be fa nit dropped the e at alec acid so ethanoic acid the common name for this is acetic acid and so once again that's the one that you'll hear more often so acetic acid and this name comes in a Latin word for vinegar because vinegar is just a dilute solution of acetic acid in water alright let's name this one down here so you want to find the longest carbon chain that includes the carbon of your carboxylic acid so that's gonna make this carbon over here carbon number one so two three four five so a five carbon carboxylic acid that would be pentanoic acid so go ahead and write pentanoic acid here so pentanoic acid and then we have a bromine on carbon four and so before bromo and so the full i you pack name would be four bromo at pentanoic acid alright let's look at this one so three carbons so this would be carbon number one two and three so a three carbon carboxylic acid would be propanoic acid but since we have a double bond present need to change the a to an e so be propanoic acid let me go and write this out so maybe proteins without e here propanoic acid like that and then for for we can just go ahead and put in a 2 here to indicate the start of the double bond so to propanoic acid we don't the worry about the stereochemistry of the double bond since that's a mono substituted double bond but for a longer carboxylic acid you would have to think about the stereochemistry alright let's do some more examples so let's look at this molecule over here on the bottom left and we can see there's a benzene ring attached to a carboxylic acid and so we've seen this before and we called it to benzoic acid so let's go ahead and start that as our parents name so we have benzoic acid right here and then if we're gonna name it as benzoic acid that gives the carbon attached to the carboxylic acid carbon number one and then we want to give our substituent the lowest number possible so so of course this is going to be carbon number two and we have a H at carbon two so it's two hydroxybenzoic acid so two hydroxy benzoic acid but Zomig acid is actually a common name but it's again use used so frequently in organic chemistry it's been incorporated into IU PAC nomenclature if we want to name this another way we could say it's it's two hydroxy or ortho hydroxy alright and then we see there's a benzene ring so two hydroxy benzene and then we have our carboxylic acid so two hydroxybenzene carboxylic acid is another ayehu pack name for this molecule you don't see people name it that way usually just because it's so long and it's it's just be much easier to say benzoic acid the common name for this molecule is salicylic acid so let me go ahead and write that so salicylic acid is famous because it's a precursor to aspirin and wintergreen so the name for salicylic acid comes from the Latin word for willow tree because you can get this compound from the bark of the willow tree and and the Greeks knew about this and it would it would reduce fevers and decrease pain and so that's of course why I also like acid was transformed into aspirin alright let's let's look at this one over here on the right and so instead of having a benzene ring we have a cyclohexane ring so this would be a cyclo hexane and now we have our carboxylic acids over here so we could say cyclohexane carboxylic acid for this one so cyclohexane almost running out of room here carboxylic acid like that so instead of saying benzene carboxylic acid its cyclohexane carboxylic acid alright so what do you do if you have two carboxylic acids in the same molecule and so that's what we have here we can see there are two carbons present so we go ahead and start by writing ethane alright so we have two carboxylic acid so we're going to use die in here so ethane die and now o ik so ethane dioic acid would be the IU pack name for this molecule the common name for this molecule is oxalic acid so no oxalic acid like that alright let's look at properties of carboxylic acid so we'll start with boiling point and so let's compare these two molecules in terms of their boiling point so over here on the Left we have acetic acid which has a boiling point of approximately 118 degrees Celsius and over here in the rights we have ethanol and the boiling point of ethanol is approximately 78 degrees Celsius so acetic acid has a higher boiling point and we can think about why by thinking about two molecules of acetic acid interacting and intermolecular forces that are present so let's go ahead and draw another molecule of acetic acids I'm going to go ahead and draw it so there's my carbonyl and then we have an oxygen and then a hydrogen and on this side on methyl group alright so there are opportunities for hydrogen bonding all right so there could be a hydrogen bond right here right because in the hydrogen bond right here so remember oxygen is more electronegative than hydrogen so oxygen gets a partial negative the hydrogen gets a partial positive and then this oxygen over here is also partially negative and so you have this opposite charges attracting right this this partially charged oxygen attracted to this partially positive charge partially positively charged hydrogen here and this is your hydrogen bond at the strongest intermolecular force alright the same thing down here so we can think about two hydrogen bonds forming for two molecules of acetic acids alright and over here on on the rights we have ethanol so let's go ahead and draw in another molecule of ethanol alright so here we have our second molecule of ethanol and we can see there's a height that could be a hydrogen bond right here so once again we have our partially negative oxygen and partially positive hydrogen partial negative oxygen like that so we have one hydrogen bond and so there's more opportunities for hydrogen bonding in acetic acid than in ethanol and so because there are more opportunities for hydrogen bonding right there's stronger forces holding these two molecules together and so it takes more energy to pull them apart and that's the reason why it has a higher boiling point all right let's think about solubility in water so and let's let's stick with thinking about acetic acid right here so we know acetic acid is soluble in water because vinegar is acetic acid in water and so if we don't have a lot of carbons right so sudoc acid has only two carbons this molecule is polar enough to dissolve in water so we could show acetic acid interacting with water right so let me go ahead and draw a water molecule right here and I'll draw a water molecule over here and so there's of course some hydrogen bonding that can go on alright so you can think about a hydrogen bond right here and a hydrogen bond right here and so acetic acid is soluble in water water is a polar molecule and acetic acid is polar enough to dissolve in water however as you increase the number of carbons in your R group right so as you increase the number of carbons to get more carbons and hydrogen's and so you get more of a non-polar character and the more the more non-polar you make this molecule the more you decrease its solubility in water so once you get past some around five or six carbons you decrease the solubility dramatically and so so that's just a little bit into the physical properties and the nomenclature of carboxylic acids