Why does the trans isomer have a lower heat of decomposition than the cis isomer?

Answer 1

Trans isomers have higher melting point because they are more stable than cis isomers. this stabality arises due to their shape, trans are strieght which allows H intermolecular forces to accure and make the trans stable.

Also depending on the R groups, if they are next to each other (in cis) repulsion might accure (specially if the R groups are large) this can lead to reduction in the melting point of Cis.

Answer 2

Trans isomers pack together better so the Van der Waals forces (intermolecular forces) between the isomers are stronger than in cis isomers; thus, the melting point of trans isomers is higher.

Answer 3

In general, the trans isomer of an alkene is more stable than the cis isomer of the same compound. The cis and trans prefixes also apply to certain substituted cyclohexanes, other specific cyclic compounds, and to many polycyclic compounds even if those compounds do not contain a double bond.

Your question asks about the "Heat of Decomposition": however, I am not familiar with that quantity, probably because it depends on the degree of decomposition in question, and therefore it is not rigorously defined as scientific terms must be.

I believe that you mean the Heat of Combustion.

To answer your question, all that matters is the difference in energy between a specific chemical compound and its combustion products - typically water, carbon dioxide, and perhaps NOx if it contains nitrogen. Imagine a vertical axis that represents a compound's potential energy. Also imagine that the potential energy increases from the bottom of the axis to the top. As you know, organic compounds release energy in the form of heat and/or light when they are completely oxidized by oxygen because the combustion products are more stable - they have less potential energy in total - compared to the compound that was burned. So, on your energy axis, the combustion products are below the compound that was burned, and the energy that was released during combustion is the difference between the potential energy of the organic compound and the combustion products. Now, if you have x grams of the trans isomer of a compound and also x g of the cis isomer of the same compound, then you have the same number of moles (and molecules) of both compounds. In the vast majority of cases, the trans isomer has a lower potential energy, which means that it starts out lower on the energy axis compared to the cis isomer. Since the combustion products are exactly the same for both isomers, the difference in energy between the trans chemical compound and the combustion products must be lower than the energy difference between the cis isomer and those same combustion products.

In alkenes, remember that the two carbon atoms double bonded to one another and the two atoms bound to each doubly-bound carbon atom (for a total of six atoms) all lie in the same plane. In the trans isomer of an alkene, there must be two identical atoms (usually hydrogen) each bound to one of the two doubly-bound carbon atoms, and those two identical atoms must be on opposite sides of the double bond, therefore the remaining two groups or atoms bound to the carbon-carbon double bond must also be on opposite sides of the double bond.

Whether the cis/trans moniker applies to an alkene, substituted cyclohexane, or to any other compound, there is usually less steric hindrance in the trans isomer compared to the cis isomer of the same compound. Steric hindrance raises the potential energy of a molecule. As a result, any stereoisomer of the same compound that has less steric hindrance will have less potential energy.

Answer 4

Cis-isomers generally have higher boiling points. The Latin prefix cis- means "on the same side." This generally means the molecule will have a greater concentration of either a dipole or dispersion forces on one side of the molecule as opposed to another. This will mean the greater probability of that molecule either being polar or having a temporary dipole, which means greater attraction between those molecules. In a trans-isomer, which means "across from," you will have a certain atom across the molecule from the other, which means often, those potential dipoles or dispersion forces will "cancel each other out," meaning less probability for attraction between molecules.

Answer 5

Actually, the cis isomer has a higher boiling point than the trans one because cis isomers are polar and therefore it requires of more heat to break the stronger intermolecular force

Answer 6

IT ISN'T!

The boiling point of trans-isomers are higher than cis-isomers because they have strong IMF

Answer 7

Trans 2-Butene actually has a lower boiling point than Cis 2-Butene.

Answer 8

The cis isomer has a higher boiling point. The cis isomer is more polar so it experiences stronger dipole-dipole interaction.