α-Farnesene is a dodecatetraene found in the waxy coa...

Question

α-Farnesene is a dodecatetraene found in the waxy coating of apple skins. What is its systematic name? Include E and Z where necessary to indicate the configuration of the double bonds.

Accepted Answer

All right. Hi everyone. So this question is asking us to consider the structure of a do Deca tetra in show up, provide its systematic name, use E and Z in naming to designate the configuration of the double bonds if necessary. And here we have four different answer choices. So here recall first and foremost that E and Z is used instead of the cist trans naming system for all keens when dealing with tri and tetra substituted all keens specifically. So this is a do Decca Trine. So we have a 12 carbon chain and four double bonds within that chain. Now, before we start talking about the identification of substituents and therefore enz nomenclature, let's first number, this carbon chain recall that the idea is to give each substituent or specifically each double bond. The lowest possible number, notably on the right side of the structure provided is one terminal a keen. So because of this, I'm going to start numbering my carbon chain from right to left and make sure that these double bonds have the smallest position numbers possible. So I would start numbering from right to left. So after numbering all of our carbons within the perry chain. The double bonds are located in carbons or starting on carbons 147 and 10. So we can expand the name provided to become though Decca 14 710 te in recall that dashes are used to separate numbers from letters and commas are used to separate numbers from each other. So now let's talk about naming and identifying substituents or any groups that are branching off of the carbon chain. The parent chain, in this case, it just so happens that there are three substituents branching off of the carbon chain. Now all three of them contain one single carbon. So all three are methyl groups. Recall that when more than one of the same substituent is present prefixes such as die, try cetera, et cetera are used to indicate their quantity because we have three metal groups before the name of the parent chain goes try methyl with no space in between. However, before the names of the substituents goes, their position numbers on the parent chain, we have one methyl group on carbon four, another on carbon eight and the other on carbon 11. So that becomes four comma eight comma 11 dash triethyl. And once again, I would place that before the name of the parent sha. So now let's talk about the nomenclature of the double bonds themselves. Now that we've covered all substituents, once again, we have four double wands, we have one in between carbons, one and two another in between carbons, four and five in between carbon seven and eight and also in between carbons 10 and 11. Now, even though there are four different alkenes or four different double bonds recall that not all of them may require E or Z designation. Consider the first and last double bonds within the carbon chain. Carbon one to be particular contains two hydrogen atoms and carbon 11 contains two methyl groups branching off of it because both of these, both of these double bonds contain at least one carbon that has two of the same substituent E or Z naming cannot apply to them. So instead, we would focus our attention on the two innermost double wants the one in between carbons four and five and the other in between carbon seven and eight. So let's consider first, the bond in between carbons four and five. Recall that we would consider the substituents that are branching off of both carbons of the double bond. The group with the highest atomic mass is given the higher priority on that side. If there's a tie, then at that point, you would continue down the substituent until you find the first point of difference. So starting off here on carbon four, branching off of carbon four is one methyl group or CH three and carbon three of the parent chain. Now, right now, there is a tie in between their atomic weights considering both substituents contain carbon. However, carbon three of the parent chain breaks the tie because it is connected to one other carbon in addition to two hydrogens, whereas the metal substituent is only connected to three hydrogens. So because of that carbon three is of a higher priority on that side of the double bond. So when considering carbon five of the parent chain, carbon five is bonded to one hydrogen and one carbon. So because carbon has a greater atomic weight, that is the higher priority on that side. So what this means is that the two priority groups on both sides of the all Ken are actually on opposite sides of the all Ken itself. So this means that the double bond in between carbons four and five is in the e configuration, but the higher priority groups are on opposite sides. So now lets consider the double bond in between carbon seven and eight starting off with carbon seven. Once again, carbon seven is connecting to one hydrogen and one carbon. Meaning that carbon is going to be the higher priority group on that side since it has a greater atomic weight than hydrogen. On the other hand, on carbon eight, we have one methyl substituent and another carbon specifically carbon nine of the per chain. Now, carbon nine of the parent chain is connected to one other carbon as well as two hydrogens. Whereas the methyl substituent is only attached to three hydrogens because of this carbon nine of the parent chain is going to be the higher priority group because the other carbon is the first point of difference compared to the methyl group. So once more, when considering the double bond in between carbon seven and eight, the higher priority groups are on opposite sides of the double bond. So at carbon seven, we also have E configuration. So now that we have the easy designation for the two double bonds that apply for it, we can place that at the very beginning of our systematic name in parentheses and separated by a dash from the rest of the name itself. So that becomes open parentheses. Four E comma seven E close parenthesis, dash 4811 tri methyl do Decca 147 10 Tetra. And this matches with option C in the multiple choice. So there you have it. And with that being said, thank you so very much for watching and I hope you found this helpful.

α-Farnesene is a dodecatetraene found in the waxy coating of apple skins. What is its systematic name? Include E and Z where necessary to indicate the configuration of the double bonds.

Key Concepts

Dodecatetraene Structure

E/Z Configuration

IUPAC Nomenclature

Watch next