hello everybody my name is Iman welcome back to my YouTube channel today we're going to continue our lecture on analyzing organic reactions last time we talked about sn2 reactions today we're going to talk about sn1 reactions to start off this video now when we were talking about sn2 reactions we presented it as a love story all right today we're going to do the same thing with sn1 but it's going to be a slightly different love story and here's the things to keep in mind all right for sn1 reactions they're going to proceed in two steps instead of one like we saw for sn2 reactions so here in the first step the leaving group is going to leave all right forming a carbocation which is an ion with a positively charged carbon atom all right and then in the Second Step the nucleophile is going to attack the planar carbocation from either sides leading to a race mixture of products now something to keep in mind here in this in this middle step all right when we form this carbocation is that there's the possibility of rearrangement all right there's the possibility of having a methyl or hydride rearrangement occur to form a more stable carbocation so here's how we can remember this in the in in this sense of a love story so the first thing you have is that the leaving group The halogen it's going to dump the carbon first all right and so then you get this carbocation all right sometimes if the molecule is not in a good head space after the breakup to deal with their loss they're going to work on themselves rearrange their thoughts all right and so what that means is okay sometimes a methyl or a hydride rearrangement occurs to form a more stable carbocation after some time the nucleophile the molecule finds a new lever and nucleophile all right so that's the second step where you have nucleophilic attack all right so loss of a leaving group happens in one step you can have the possibility of carbocation rearrangement and then your nucleophile attacks as for kinetics for this reaction all right what you're going to notice is that the rate equation only depends on the concentration of the substrate making it unimolecular hence why this is called a unimolecular nucleophilic substitution reaction all right now with unimolecular processes like sn1 there is the possibility of rearrangement after the leaving group dips just like we said it's important to reiterate all right now in short your sn1 reaction it proceeds in two steps your first step the leaving group group leaves forming a carbocation all right in the Second Step the nucleophile attacks that plane of carbocation leading to a race mixture of products sn1 reactions they prefer more substituted carbons because the alkyl groups can donate electron density and stabilize the positive charge of the carbocation and then the rate of sn1 reactions is dependent only on the concentration of the substrate this is all to contrast what we talked about sn2 reactions sn2 reactions they proceed in one step the nucleophile attacks at the same time as the leaving group leaves the nucleophile must perform a backside attack which leads to an inversion of stereochemistry all right and note that the absolute configuration is changed if the incoming nucleophile and the leaving group have the same priority in the molecule sn2 reactions they prefer less substituted carbons because the alkyl groups create steric hindrance and they inhibit the nucleophile from accessing the electrophilic substrate carbon the rate of sn2 is dependent on the concentration of both the substrate and the nucleophile with that we have covered nucleophilic substitution reactions and we can move into our third objective our third objective is all about oxidation reduction reactions reactions that involve the transfer of electrons from one species to another can be classified as oxidation reduction reactions or in other words redox reactions no the law of conservation of charge it states that electrical charge can neither be created nor destroyed so an isolated loss or gain of electrons can't occur and this allows us to start to Define oxidation and reduction oxidation is loss of electrons and reduction is gain of electrons and they must occur simultaneously leading to an electron transfer that's called a redox reaction now another way of saying this is that oxidation is losing electrons reduction is gaining electrons all right and where the actions where oxidation and reduction occur are are also called redox reactions because oxidation cannot occur without reduction all right now in let's write those definitions now all right so we have oxidation we have reduction oxidation is loss of electrons reduction is gain of electrons all right now we have other ways of framing the definition for oxidation and and reduction and in organic chemistry actually makes more sense to think of oxidation as increasing the number of bonds all right to oxygens or other heteroatoms heteroatoms are atoms besides carbons and hydrogens now similarly it makes more sense to think of reduction as increasing the number of bonds to hydrogens all right so this is another frame of reference for how we want to Define oxidation and reduction all right now something else that's important all right is that we can Define oxidation as an increase in oxidation state all right and reduction as a decrease in oxidation state all right fantastic so oxidation refers to an increase in oxidation state reduction refers to a decrease in oxidation state so now we have these variable definitions that we can reference when we talk about oxidation and reduction now something else that's important to Define is oxidizing agents and reducing agents so we said that when a substance gains electrons and is reduced it causes something else to lose electrons and be oxidized and so therefore the substance that is reduced is called the oxidizing agent all right so the substance that's reduced is called the oxidizing agent likewise when a substance is oxidized it causes something else to gain electrons and be reduced therefore the substance that's oxidized is called the reducing agent all right and it's important that we are familiar and comfortable with this terminology for the MCAT now we're obviously going to want to elaborate on these definitions for ochem relevance all right and so the first thing we're going to focus on is oxidation reactions and the oxidizing agents that help those reactions occur all right now we mentioned that oxide oxidation refers to an increase in oxidation state all right now also we we also said the oxidation is an increase in the number of bonds to oxygens or heteroatoms all right so now something that's important for the MCAT is to be familiar with these reactions that we see here all right these are oxidation reactions and common oxidizing agents all right now I I can tell you that these are important to know for the MCAT so go ahead and make sure that you memorize them but also it's not just memorizing it's also making note of two things here and those themes are that oxidation reactions tend to feature an increase in the number of bonds to oxygen and that oxid oxidizing agents they often contain Metals bonded to a large number of oxygen atoms all right so those are two important Concepts that you should keep in mind when you're trying to approach remembering these reactions now looking at these you can also begin to organize the different functional groups by levels of oxidation all right and also it's going to help you understand how you can move from you know primary alcohols to aldehydes to ketones to carboxylic acids all right where carboxylic acids is your highest level all right of oxidation so here if we look just quickly going over a couple of these reactions all right you have you see this primary alcohol all right it's oxidized to an aldehyde all right and you also see that you can go from primary alcohol all right to carboxylic acid all right so primary alcohols they can be oxidized by one level to become aldehydes or they can be further oxidized to form carboxylic acids all right this reaction commonly proceeds all the way to the carboxylic acid level when you're using strong oxidizing agents such as chromium trioxide or sodium or potassium dichromate or even something like potassium permanganate all right like you see written here all right but if you only want to stop at the aldehyde level all right you want to use specific reagents all right that are not the strong oxidizing agents or not at least the strongest oxidizing agents you can use something like per uh pyridinium chlorochromate also known as PCC which is what you see here all right so you can go from primary alcohol to aldehyde using a reagent like PCC or you can go from primary alcohol all the way to carboxylic acid using strong oxidizing agents like potassium permanganate potassium dichromate or sodium dichromate all right so things of that nature you can also go from secondary alcohol to Ketone using PCC all right now if you're at alt if you have an aldehyde and you want to go to carboxylic acid you're going to want to use your strong oxidizing agents like potassium permanganate um like potassium permanganate all right you can also go from an alkane to carboxylic acid so you see here that's an alkene going to carboxylic acid you're going to want to use a strong oxidizing agent like potassium permanganate for this kind of reaction as well all right so those are just a couple of oxidation reactions that we should definitely be familiar with all right and like we said really the success to understanding and memorizing these reactions is recognizing two important things and that's oxidation reactions tend to feature an increase in the number of bonds to oxygens and that oxidizing agents often contain metals that are bonded to a large number of oxygen atoms now we can similarly all right talk about reduction all right we can talk about reduction and we can talk about reducing agents and their reactions all right so reduction refers to a decrease in oxidation state all right or in other words like we wrote in our diagram we could think of reduction as an increased number of bonds to hydrogen atoms all right now we can look at some of our more common reduction reactions and common reducing agents that we need to be familiar with for the MCAT all right things to to remember here is that good reducing agents are going to include sodium magnesium aluminum and zinc which have low electronegativities and ionization energies metal hydrides like sodium hydride lithium aluminum hydride sodium Boron hydride are also good reducing agents because they contain right the hydride ion H minus all right now looking at these reactions you can see that aldehydes and ketones will be reduced to primary and secondary aldehydes all right they can they can you can see here that your aldehyde and your Ketone can be reduced to primary and secondary alcohols respectively this kind of reaction it's exergonic but it it precedes slow without a catalyst amides also can be reduced to amines using lithium aluminum hydride all right this same reducing agent will reduce carboxylic acids to primary alcohols and Esters to a pair of alcohols all right and that's all shown here in this figure again make sure to be familiar with these all right it's you know it's not about memorization or at least memorization becomes easier when you can recognize that reduction reactions tend to feature an increase in the number of bonds to hydrogen and reducing agents often contain Metals bonded to a large number of hydrides all right with that we've completed objective three we're gonna stop here in the next video we're going to cover our last two objectives that that's going to be chemo selectivity and also a step-by-step guide to problem solving organic chemistry reaction problems let me know if you have any questions comments concerns down below other than that good luck happy studying and have a beautiful beautiful day future doctors