Arrange the following compounds in order of increasing rate of acidcatalyzed hydration: ethene,

Arrange the following compounds in order of increasing rate...

Key Concepts

Acid-Catalyzed Hydration Mechanism

This concept involves the overall process by which an alkene reacts with water in the presence of an acid catalyst. The first step of the mechanism is the protonation of the alkene to form a carbocation intermediate, which is then attacked by water. The rate of the reaction is largely determined by the ease of formation and stability of the carbocation in the initial step.

Carbocation Stability

Carbocation stability is pivotal in many acid-catalyzed reactions. More substituted carbocations are typically more stable due to better distribution of positive charge through hyperconjugation and inductive effects. The stability of the carbocation intermediate influences the reaction rate, with more stabilized intermediates forming faster and leading to an accelerated overall reaction.

Hyperconjugation

Hyperconjugation refers to the stabilization of a carbocation through the delocalization of electrons from adjacent C–H or C–C ?-bonds into the empty p-orbital of the carbocation. This electron donation helps to disperse the positive charge over multiple atoms, thereby stabilizing the carbocation intermediate and facilitating a faster reaction in processes like acid-catalyzed hydration.

Inductive and Resonance Effects

Inductive and resonance effects are general electronic factors that influence carbocation stability. Electron-donating groups can stabilize a positive charge by pushing electron density through sigma bonds (inductive effects) or through overlapping orbitals (resonance effects), while electron-withdrawing groups have the opposite effect. The balance of these effects in the molecule dictates how readily the carbocation intermediate is formed during the hydration process.

Neighboring Group Participation

Neighboring group participation involves the stabilization of intermediates through interactions with nearby functional groups or structural elements, such as cyclopropyl groups. These groups can provide additional stabilization by delocalizing the charge through their unique bonding interactions, often leading to enhanced reactivity compared to systems lacking such groups. This concept is significant when considering reactions where unusual substituents alter the conventional stability trends of intermediates.

Transcript

00:01 In this video, we're going to be talking about acidity and the factors that affect acidity.

00:06 And here on screen, i have generally just a general list of factors that affect acidity.

00:12 This is my five.

00:13 It may change depending on where you look.

00:16 Or maybe if you ask other people, the factors affect acidity.

00:19 This is my ranking.

00:21 And so for the presence of this video as well, some of these factors go more into the organic chemistry aspect.

00:30 So we're not going to really talk about all of them.

00:33 We're really just honestly going to be focusing on two that are more for general chemistry here.

00:37 So factors one and two are more relevant to what we're going to be talking about.

00:44 But factors three, four, and five more for the knowledge that you'll need for organic chemistry if you do study that course.

00:54 So for the factors that affect acidity, we're going to be looking at electronegativity and atomic size.

00:59 And more specifically for this video, we're looking at factor number one, which is electronegativity.

01:06 But nonetheless, electro negativity.

01:08 So what is electronegativity? if we remember the definition, it is where an atom has the tendency to pull electrons towards itself, right? so we know that there is a trend in the periodic table.

01:20 And if we want to draw the trend, just more or less over here, the trend goes up the periodic table and across.

01:27 So that's going to, this shows the movement, or this shows the trend of increasing electronegativity.

01:33 It goes up and then towards the right, with fluorine being the most electromagnetic element.

01:39 So if you have a compound that has election negative atoms present, that's going to increase the acidity of that particular compound.

01:48 And of course, if you have less electronic elements, it's going to decrease the acidity as well.

01:53 And so that kind of moves us with the second factor, which may not be super relevant with the types of examples that have written here on the board or on the white board, but it is atomic size.

02:07 And examples would be if we're thinking about our assets, for example, our assets that we take from the halogens, for example, like h -i, h -f, hbr, for example.

02:22 And so when you have the size in which it contributes to acidity is that the bigger atomic radius or the very atomic size is going to increase acidity.

02:33 So if we want to, for example, if we want to compare the acidity between hf and then versus, for example, h .i.

02:44 If you want to also take a look at your product table, you'll see that floring is higher on that particular column in which it is.

02:53 Place it's higher i mean we if we know the trend for atomic size is that atomic size if we go down the periodic table it is going to increase so it's going to be just like so if this is how atomic size increases it goes down the periodic table and so we know that iodine is going to be much bigger in atomic rate in terms of atomic radius it's much bigger than fluorine and so because the the size of iodine is considerably much bigger in comparison to hydrogen.

03:27 It is much easier, essentially, for the bond between hydrogen and iodine to break.

03:35 There is less stability because the radius is just so big.

03:40 There's not a strong bond between hydrogen and iodine.

03:43 And so it makes this acid more readily dissolvable in water, for example, versus something like hf, fluoric acid.

03:53 The bond is more tight.

03:55 It's closer because fluorine has a much smaller atomic radius.

04:00 The bond is a little bit stronger.

04:02 It's held more tightly.

04:03 So it won't this associate as readily in water as in comparison to hydro -iodic acid...