Which stereoisomer of 3,4-dimethyl-3-hexene forms (3S...

Question

Which stereoisomer of 3,4-dimethyl-3-hexene forms (3S,4S)-3,4-dimethylhexane and (3R,4R)-3,4-dimethylhexane when it reacts with H₂, Pd/C?

Accepted Answer

Hey, everyone. And welcome back in today's video. We're going to identify the stereo isomer of dibromm be two in which produces two S S 23 dibromm butane and two R three R 23 di bromo butane upon the hydrogenation using hydrogen gas with palladium over carbon. So let's suppose that the stereo isomer that we are looking for is X. Now because it's an, we have a suffix E, we can either have a Z isomer or an E isomer. We want to identify whether it's C or E. Now, the problem stays that we're performing a hydrogenation reaction where we're using high chain gas with palladium over carbon. And we are forming two products. Both of them are di bromo Beane compounds. So we can draw a four member chain for each. And now we understand that carbons two and three, they have two BROMO substitutes, but we don't really know what sort of stereo chemistry we have unless we assign it using the conning or log rules. So first of all, let's add those bromine atoms on solid lines and let's adjust our bonds. Now, to do that, we need to analyze chiral positions two and three in each of the two structures. According to the Kellog rules, we're going to analyze the first carbon of the first structure are basically carbon number two to be more accurate. Now, let's draw that carbon and let's draw the substitutions Barnett said. So it has bromine attached to it. Then on the right side, it has carbon, bro, are basically carbon hydrogen. Then bro and a metal group CH 3. On the other hand, we have a metal group and then we also have hygiene attached to it. So let's assign priorities. Bromine gets priority 1 because it's it has the highest atomic number followed by the second priority of the C H PR group because it's carbon which is directly bonded to bromine as opposed to carbon directly bonded to hydrogen. So metal group gets priority number three. Hydrogen gets priority number four because it has the lowest atomic number. Now, essentially, if we think about assigning those priorities to our actual structure, we can stay that broom in guest priority one, C H B R gets priority two. Metal gets priority three hyen gets priority four. So we have an implicit hyen if we assign a rotation directly and we trace our path from 1 to 2-3, we get a clockwise rotation and that will be R as long as hygiene is pointing down. So let's suppose that hydrogen is pointing down to make it valid. We always want to make sure that hygiene is pointing away so that the rotation can be assigned directly because priority number four must be pointing down. That means bro will be pointing up on a wedge. So we got our configuration, this is consistent with the second structure and we want to make sure that the third position is R as well. And do that. We are going to think about car number three and the substitutions are pretty much exactly the same, right. So we can just say that bro gets priority one. We, for simplicity, we can also erase our priorities for the previous carbon. We can just say that position number two is R. And now for the third position, bro gets priority one. C H pr gets priority two metal gets priority three. And if we trace our path from 1 to 2-3, we get a clockwise rotation, which is indeed R as well. So that means hydrogen must be pointing down for it to be valid. And Bromine will be pointing up on a wedge. Wonderful. So we can erase our priorities here because we have got our 2 R 3 r structure. And now to get two S3 S, we are just going to swap priorities one and four. So the two bromine atoms will be just pointing down because in the first structure, they are both pointing up. So for the second structure, let's add two dashes for each Bromine because in the first structure, we have two wedges and now let's make it a bit neater, right? Let's just eliminate our first structure and we draw it in a more readable way. So we have a four member chain with two bromo substituent or basically two bromo groups running up. We have successfully got our products. And now we have to remember that hydro hydrogenation follows the sun addition, meaning the two hydrogen atoms are bonded to an alkene from the same side. So if we expand our implicit hydrogen atoms in the first structure, the two hydron atoms are on two dashes and then they are on two wedges in the second structure because the two hydrogen atoms are already in some arrangement in each structure specifically, they are on two dashes in the first structure. That means they are sent to each other. And then the second structure they're also sent to each other because they're on two wedges. That means we can essentially remove these hydrogen atoms and place a double bond between carbons two and three. To get our, in each case, we get the following our four membered chain, two bromo subs chances. And then we're placing a double bond between carbons two and three without performing any rotation because the two hydrogens are already sent to each other. So we don't need to rotate our bond. And similarly, for the second structure, that's exactly the same thing. We get our four member chain, our double bond and then our bromo substituent. So we can state that the alkin that is required for this hydrogenation is an E isomer because the two bromo substations are on opposite sides of the double bond. So we are going to choose E as our final answer. And basically, since we got our structure, it's just sufficient to draw one because they're equivalent to each other. And we can state that the identity of X is E 23 di bromo be two in. So we got our answer, that's the E E and we are going to label it in a green box based on the answer that we got, we may conclude that the correct answer to the multiple choice question is a Thank you for watching.

Which stereoisomer of 3,4-dimethyl-3-hexene forms (3S,4S)-3,4-dimethylhexane and (3R,4R)-3,4-dimethylhexane when it reacts with H₂, Pd/C?

Key Concepts

Stereoisomerism

Hydrogenation

Chirality and Enantiomers

Watch next

Which stereoisomer of 3,4-dimethyl-3-hexene forms (3S,4S)-3,4-dimethylhexane and (3R,4R)-3,4-dimethylhexane when it reacts with H2, Pd/C?

Key Concepts

Stereoisomerism

Hydrogenation

Chirality and Enantiomers

Watch next

Which stereoisomer of 3,4-dimethyl-3-hexene forms (3S,4S)-3,4-dimethylhexane and (3R,4R)-3,4-dimethylhexane when it reacts with H₂, Pd/C?