Which substitution reaction takes place more rapidly? d. CH 3 CH 2 Cl + I − or CH 3 CH 2 Br + I −

Welcome back, everyone or the following substitution reactions determine which would react faster. One Chloro T methyl propane with the iodide anion or one bromo T methyl propane with the iodide anion. So first of all, let's draw the two structures that we have in question, each of them corresponds to a substituted propane specifically for the first structure. We're going to add our methyl group and our Chloro group. And for the second structure, the main difference is that instead of the Chloro substituent, we now have the bromo substituent, each of them is treated with the iodide anion. The iodide N nine is a strong nu file because we have a negative charge on iodine. And if that's a strong nuclear file, let's abbreviate that S S N. And in addition to that, we have the primary substrate. In each case, we can conclude that in each case, we are observing an essence two reaction because we're dealing with a substitution. So now in an essence reaction, the nuclear attacks, the electrophysics center followed by the loss of the leaving group. So let's throw the mechanism for each reaction. And now we can control the two result on products, which will be exactly the same. In addition to that, for the first reaction, we're forming the chloride and ion. And for the second one, we're forming the bromite and ion. Let's recall that in essence, reaction rate increases whenever we choose a better living group. So we want to determine which one of the two is a better living group because that's the only difference. We have our chloral substituent and we have our bromo substituent. And because both of them are halogens, it's size dependent, the radius of the broom atom is greater than the radius of the chlorine atom. Because whenever we go down the group in the periodic table, the atomic radius increases and the greater the radius, the better the leaving group is right. Because when we think about the formed chloride and bromide ions, we know that a bigger base will be able to stabilize the negative charge better, right? Because it's more polarized. So the negative charge is not so dense on the bromite and ion because it's spread out across a larger surface area of the bromite and Ron. So we may simply conclude that between the two reactions, the second one will react faster because it has a better living group. Due to the fact that the atomic radius of bromine is greater than the atomic radius of chlorine, the second reaction would react faster. Thank you for watching

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1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
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7. Substitution Reactions

Good Leaving Groups

Organic Chemistry

7. Substitution Reactions

Good Leaving Groups

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3:31 minutes

Problem 14d

Textbook Question

Which substitution reaction takes place more rapidly?
d. CH₃CH₂Cl + I⁻ or CH₃CH₂Br + I⁻

Verified step by step guidance

Step 1: Understand the type of substitution reaction involved. This problem refers to nucleophilic substitution reactions, specifically SN2 reactions, where the nucleophile (I−) attacks the electrophilic carbon bonded to the leaving group.

Step 2: Evaluate the leaving group ability. In SN2 reactions, the rate depends significantly on the leaving group. A better leaving group will make the reaction proceed more rapidly. Compare Cl− and Br− as leaving groups. Br− is a better leaving group than Cl− because it is larger and more polarizable, making it more stable after leaving.

Step 3: Consider the nucleophile. I− is a strong nucleophile due to its large size and high polarizability, which makes it effective in attacking the electrophilic carbon in both cases.

Step 4: Analyze the steric hindrance. Both CH3CH2Cl and CH3CH2Br are primary alkyl halides, meaning they have minimal steric hindrance, which favors the SN2 mechanism. Therefore, steric hindrance does not significantly affect the comparison in this case.

Step 5: Conclude based on the leaving group ability. Since Br− is a better leaving group than Cl−, the reaction involving CH3CH2Br + I− will take place more rapidly than CH3CH2Cl + I− under identical conditions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. The rate of these reactions can depend on the nature of the leaving group and the strength of the nucleophile. In this context, the reaction speed is influenced by the bond strength between the carbon and the leaving group, which affects how easily the leaving group can depart.

Leaving Group Ability

The ability of a leaving group to depart from a molecule is crucial in determining the rate of nucleophilic substitution reactions. Bromide (Br−) is generally a better leaving group than chloride (Cl−) due to its larger size and weaker bond strength with carbon. This means that reactions involving bromides typically proceed faster than those involving chlorides, all else being equal.

SN2 Mechanism

The SN2 mechanism is a type of nucleophilic substitution that involves a single concerted step where the nucleophile attacks the carbon atom from the opposite side of the leaving group. This results in a transition state where both the nucleophile and the leaving group are partially bonded to the carbon. The sterics and the strength of the leaving group play significant roles in the reaction rate, making the SN2 pathway faster for substrates with better leaving groups.

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