Strawberry growers have used large quantities of methyl bromide (...

Question

Strawberry growers have used large quantities of methyl bromide (b.p. 4 °C) to sterilize the soil before planting their crops.

Like some of the freons, methyl bromide can diffuse up into the stratosphere, where it damages the protective ozone layer.

Agricultural chemists have suggested using methyl iodide (b.p. 43 °C) as a replacement for methyl bromide.

1. Why is methyl iodide likely to be more toxic to agricultural pests (and people) than methyl bromide?

2. Why is methyl iodide less likely to reach the stratosphere than methyl bromide?

Accepted Answer

Hi everyone. A little chloride is an important industrial compound. Large quantities of a low chloride are used to produce epic laurel. High trend a precursor to many epoxy resins. Alot chloride reacts with many nuclear files to give nuclear Felix substitution reactions. And al Kill Hayley. That is similar in structure to a low chloride is proto chloride. If both of these compounds react with sodium meth oxide, which is less likely to be consumed first. Now, we know that there's a lot of information here and as you know, there are many chemistry problems where they give us a lot of information regarding the context. But let's just concentrate on the most important parts here. We wish to understand which one of them is less likely to be consumed first. And to answer the question, we have to realize that we're dealing with kinetics which reaction is foster which one of them is slower. So let's concentrate on that Now, let's draw the two structures in question. One of them is a little chloride. This is the structure of a little chloride and then we have propel chloride which looks very similar just as the problem suggests. The problem also states that they both react with sodium with oxide, sodium is an ion spectator. So we we shouldn't worry about it. We just know that if we think about sodium with oxide, N A O CH three. This ionic compound dissociates and the sodium ions and meth oxide and ions. So the actual one that reacts is the so the meth oxide and I on that soc three negative in each case because it's a charged nuclear file that has a negative charge and oxygen. That means it's strong. So the reaction in question is an essence a reaction. Knowing that this is an essence to reaction, we wish to compare the reaction, wait for the two. So in each case we have exactly the same strong nuclear file and the strength of that nuclear file is exactly the same because in each case that's the meth oxide. The substrate in each case is primary because chlorine is attached to a primary carbon atoms to the electra Felix center only has one neighboring carbon atom. Now the leaving group is exactly the same. That's chlorine. So the main aspects for a substitution reaction. Whatever influences the reaction rate, all of these three aspects are exactly the same. The nature of the nuclear file, the leaving group and the nature of the substrate. However, if you look at these two structures, the main difference is that a little chloride actually has this double bond over here while pro bill doesn't. So we have two sp two hybridized carbons here. While here we have sp three hybridized carbons and now this is actually the major reason why they have different reactivity and different reaction rate. Specifically sp two hybridized carbons here have pi orbital's and these pi orbital's forming the pI system overlap with the orbital's of the nuclear file at the time of the nuclear attack. So when the nuclear file attacks and starts forming the bond simultaneously breaking the carbon chlorine bond? There's a transition state formed which is stabilized by the presence of these p orbital's and as a result the transition state is stabilized by the presence of the pie orbital's. So the transition state is formed is stabilized by the presence of these orbital's. While if you look at the sp three carbon atoms, inappropriate chloride, there's nothing that stabilizes that transition state. So the transition state is less stable and as a result and a little chloride would react faster and profile chloride would react slower. In addition, there are two more aspects which are not so significant but they are also worth mentioning. One of them is the stereo hinderance aspect. Notice that specifically these two carbon atoms have to hae jin's and three high jeans over here while there's only one hygiene here and to hae jin's over here. Since anil chloride is less hysterically hindered according to the sn two reaction rate less hysterically hindered electro files are more likely to be attacked at a quicker rate. So that's another reason. And the third reason is that the double bond actually withdraws these electrons, making the electra Felix center here more electoral positive, more partially positive than this electro file over here which also directly affects the reaction rate and makes a little chloride react faster than propel chloride. And as a result going back to our original question, which one of them is likely to be is less likely to be consumed first, meaning which one of them reacts slower, and the answer is propel chloride. Now dad's our final answer. The correct answer for the multiple choice question is B and in case you have any questions, feel free to leave your message down below.

Key Concepts

Toxicity of Organohalides

Volatility and Boiling Points

Atmospheric Lifetime and Degradation

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