When maleic acid is heated to 200^∘ C, it loses water and...

When maleic acid is heated to $200^{\circ} \mathrm{C},$ it loses water and becomes maleic anhydride. Fumaric acid, a diastercomer of malcic acid, requires a much higher temperature before it dehydrates; when it does, it also yields maleic anhydride. Provide an explanation for these observations. FIGURES CANT COPY

Key Concepts

Activation Energy

Activation energy is the minimum energy that molecules must possess to undergo a chemical reaction. The cis isomer has a lower activation energy for cyclization due to the favorable proximity of the reactive groups, leading to dehydration at a lower temperature. Conversely, the trans isomer requires a higher temperature because the relative positioning of its groups creates a higher energy barrier for the cyclization process.

Stereochemistry

Stereochemistry refers to the spatial arrangement of atoms within a molecule. In the context of the problem, cis (maleic acid) and trans (fumaric acid) isomers have different spatial arrangements, which significantly influence how easily they can undergo intramolecular reactions. The cis configuration allows functional groups to be positioned closer together, facilitating reactivity, while the trans configuration does not, leading to different reaction behaviors.

Intramolecular Cyclization

Intramolecular cyclization is a reaction in which a molecule forms a ring through a reaction between two functional groups within the same molecule. For cis isomers like maleic acid, the required groups are in proximity, making it easier to eliminate a molecule of water and form a cyclic anhydride. In contrast, the trans isomer's geometry hinders the formation of a similar cyclic transition state, requiring higher temperature to achieve a comparable reaction.

Transcript

00:04 When malayic acid is heated at 200 degrees celsius, it forms malayic anhydride, which is this molecule right here.

00:20 And this makes sense because, well, if a molecule with two carboxylic acids is going to heat up, it will form an anhydride.

00:32 And what it really is is two things.

00:36 It's a formation of an anhydride, of anhydride, which is a derivative of a carboxylic acid.

00:48 And the second thing, although it's not entirely clear just from the get -go, but it is, in fact, a ring closure.

01:00 And a good thing to note here is that when it comes to ring closure, if there are less than, suppose like less than nine carbons, less than nine carbons, the most stable double bonds that will be in rings are going to be cis bonds, cis alkenes.

01:28 And that's only for ring systems.

01:31 Nine to about 12 carbons is an equal stability, and anything greater than 13 carbons, has trans alkenes.

01:49 And that's a good thing to know.

01:51 And what i mean by this, or not exactly specifically carbons, but more members of the ring.

01:58 Like, for example, oxygen would be included.

02:00 One, two, three, four, five.

02:03 Five member ring, a cis double bond would be really stable for a five member ring.

02:10 However, when we are treating fumaric acid, which is just a stereoisomer of malayic acid, we end up getting the same product, but it requires more heat.

02:24 And the reason behind this is, firstly, this is a cisalcane, and that is also a cisalcine...

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