The energy difference between cis- and trans-but-2-ene is about 4...

Question

The energy difference between cis- and trans-but-2-ene is about 4 kJ/mol; however, the trans isomer of 4,4-dimethylpent-2-ene is nearly 16 kJ/mol more stable than the cis isomer.

Explain this large difference.

Accepted Answer

welcome back everyone says B two in. And transmute to in have an energy difference of four kg joules per mole. On the other hand, the trans size murder of 2 to 55 detrimental hex three in has about 40 kg per mole lower energy than the si sizemore explained the reason behind this very high stability of the trans eyes murder of 2 to 55 detrimental hex three in. Now, first of all, let's just draw the structures of says beauty in and trans beauty in to discuss the aspects behind the ALc instability. Now, if we need a B team, we draw a double bond to make sure that we get the right item, ours and the cis item are essentially implies that our substitutions are on the same side of the of the double bond. So you can either place to metal groups pointing up or down. It doesn't really matter, don't worry about it, notice that this is six beat to it and we have a double bond starting at position two A four carbon chain and the two substitue ints to metal substitutions pointing up. So this is our version now to get the trans I Zimmer, we essentially want to allocate our methyl groups on the opposite sides of the double bond. So we are adding two methyl groups pointing in different directions. So that be our trans. Now the energy difference between them is four kg joules per mole. And simply recall that trans customers are more stable because of the minimized hysteric interactions. Notice that the substations in the system is um Are they directly interact in the distance between them is much lower than the distance between these two method groups in the trans I. Zimmer. So essentially what we want to state here is that generally trans eyes murders are more stable at least if we speak about the linear chains than cysts tumors. However, if we look at our next structure to to 55 detrimental hex three in, we are ready to draw the two eyes mars. If we draw this this version of it, we have the double bond starting at position three. So these are our carbons three and 4 and then we have two more carbon atoms and two methods responded to position two as well as two methyl groups bonded to position five. So this is our sixth version of 2 to 55 the metal hex rian. And similarly, if we draw our trans version, the trans is more will essentially have the submissions on the opposite sides with respect to the double bond. So this is our trans ISA. The energy difference as the problem suggests, is 40 kg per mole, which is 10 times greater than the energy difference between six entrances MERS of beauty to in. So this is a very significant difference. Now we already know that the trans eyes murders of course more stable. But what is the main reason which causes such a high difference instability. Notice if you look at the relative size of these groups. Methyl groups. The two suppositions for the disposition are small. They only consist of a carbon atom with three small hydrogen atoms, whereas for the third beetle suspicions, that's how you can think about it. We have three methyl groups over here and another three over here. So hysterical reactions between these two methyl groups are much greater than hysteric interactions between these two small metal groups. And therefore because these groups are hysterically hindered, large or bulky, you can use whatever synonym you prefer here. That's fine. They're bulky large or hysterically hindered. Substitue ints compared to the method groups that we analyze here with an increase in size, hysteric interactions increase and therefore we see such a high energy difference making the trans eyes um are much more stable. That said, the correct answer for this multiple choice question is D and if you have any questions, feel free to leave them down below. Thank you for watching this video.

The energy difference between cis- and trans-but-2-ene is about 4 kJ/mol; however, the trans isomer of 4,4-dimethylpent-2-ene is nearly 16 kJ/mol more stable than the cis isomer. Explain this large difference.

Watch next