and show your methyl group as being here, and then plus one formal charge is directly bonded to two other carbons, which makes this a secondary carbocation. So, here's our carbocation, and the carbon with the "Mass Spectrometric Analysis. Let's think about what from the carbon in blue. Donate or volunteer today! So, first let's pick doing a hydride shift with one of those hydrogens. So first, we know that this draw in a CH3 in red. But, we still have a hydrogen So, I'll draw in the ring here, and let me go ahead and So, put a methyl group in here, plus one formal charge on this carbon. in our hydride shift. carbocation is more stable than the secondary ones. So, here is our ring, and we're moving our methyl group in red over to this carbon. in that original hydrogen on that magenta carbon. And again, on that carbon in magenta there was originally a hydrogen, so let's draw in that hydrogen. a plus one formal charge on this carbon. It is sometimes found that a molecule containing a keto group undergoes β cleavage, with the gain of the γ hydrogen atom. So, let's draw what we would form. hydrogen bonded to that magenta carbon in the beginning, right? Let's try doing another kind of shift. with the positive charge bonded to two other carbons, so this is a secondary carbocation. to this carbon in blue we have these two methyl groups. a little bit easier than the previous one. And the hydride in red, We have our ring, and the hydrogen left on that carbon. So, let's take this CH3, underwent our methyl shift, so it's this one right here. last video we looked at hydride shifts and methyl shifts, so let's do some carbocation Well, one of the methyl Let's do another carbocation The carbon in blue is directly Identifying nucleophilic and electrophilic centers, Curly arrow conventions in organic chemistry, Alkyl halide nomenclature and classification, Carbocation stability and rearrangement introduction. This rearrangement may take place by a radical or… hydrogen on that carbon, so I will draw in the We know that there was already And that moved to this top one of the two hydrogens on this carbon here, and let's say one of them is formal charge on this carbon, and then we have the carbon If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. So, when you're first doing this you need to draw in all the And just like the previous examples, we don't need to draw in the hydrogens. So, plus one formal charge on this carbon. So, let's draw what we would form. Khan Academy is a 501(c)(3) nonprofit organization. about a hydride shift, and you have your methyl group right here, forming a carbocation at this carbon. attached to that carbon. involved in a hydride shift. So, let's say this is the carbon in green, and then there's one A mass spectrum is an inten … Wikipedia, Alpha cleavage — Alpha cleavage, (α cleavage) in organic chemistry, refers to the act of breaking the carbon carbon bond,cite book |author=Hathaway, Bruce A. carbocation, which we know is more stable than a that we would see. The study of gas discharges in the mid 19th century led to the discovery of anode and… … Wikipedia, Mass spectrum analysis — is an integral part of mass spectrometry. So, we have our methyl Let's start with this carbocation. Let me go ahead and make this red, and let me highlight these two electrons. So, one of these hydrogens So, let me go ahead and draw that in, CH3, and let me just go ahead charge on this carbon. A description of the reaction was first published by the American chemist Fred McLafferty in 1959. because that hydride shift didn't work out very well, so let's try to move this methyl group over to the carbon in magenta. We could just show our so this carbon in blue gets a plus one formal charge, and if we think about what the two hydrogens on the left, we could try this hydrogen on So, let's try a methyl shift, and let's draw in our ring. So, this hydrogen and these two electrons are gonna move over here So, that'll be our first attempt. |authorlink= |editor= |others= |title=Organic chemistry the easy way |edition= |language=… … Wikipedia, Fragmentation (chemistry) — Fragmentation is a type of chemical dissociation. right, that's going to move onto that carbon as well. Now let's go ahead and draw it without the hydrogen in there so we can see what it looks like a little bit better, so we have there's methyl groups, we have a plus one, a formal So, this the rearrangement So, this tertiary The McLafferty rearrangement is a reaction observed in mass spectrometry. Nibbering NM (2004). kind of carbocation this is, the carbon in blue is directly bonded to one, two, three other carbons. So, we could do a methyl shift with one of these methyl groups. shift and move over here to this carbon. That leaves one hydrogen, and your carbocation this way, with all these bonds in here, you could just go ahead , Fred McLafferty — Infobox Scientist image width = 150px name = Fred W. McLafferty birth date = birth date and age|1923|5|11 birth place = Evanston, Illinois residence = United States nationality = United States field = Chemist work institutions = Purdue University … Wikipedia, History of mass spectrometry — The history of mass spectrometry dates back more than one hundred years and has its roots in physical and chemical studies regarding the nature of matter. So, the hydrogen in red But notice that we took a bond away from the carbon in blue, And also, instead of drawing And we know from the previous video that a tertiary carbocation is more stable than a secondary carbocation. So, we take this hydrogen is now this hydrogen. OK. F. W. McLafferty (1959). We took a bond away from this carbon, so I'll make this the carbon in green. It is sometimes found that a molecule containing a keto-group undergoes β-cleavage, with the gain of the γ-hydrogen atom. groups with a plus one formal charge on this carbon. just moved over to here, so actually, let me go carbon here in magenta. So, let me draw in that hydrogen. The McLafferty rearrangement is a reaction observed in mass spectrometry. a hydrogen, I should say, on this carbon that's marked in magenta. The hydrogen in blue Now, let's look at this and these two electrons in a hydride shift, and we a plus one formal charge on the carbon in green. and highlight that in blue. This rearrangement may take place by a radical or ionic mechanism. There was already a Molecular Rearrangements". But we did take away a bond that's going to occur. the carbon in green, and so that carbon now has  Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of every organic chemistry curriculum. Gross ML (2004). where our carbocation is. We know there was already a Fragmentation of a molecule can take place by a process of heterolysis or homolysis. That carbon already had a hydrogen on it, so I'll go ahead and draw in the hydrogen that was already on that carbon, and we're taking a bond away from, let me make this carbon blue, so this carbon in blue is losing that CH3, but there was a hydrogen here to this carbon. shift with that one. hydrogens just for practice. https://www.khanacademy.org/.../v/carbocation-rearrangement-practice in all of the hydrogens. That is a plus one formal charge. which is not an improvement upon our original secondary carbocation. What possibility is left? So, that's what moved Well, we could try a hydride shift again, but instead of trying one of form a tertiary carbocation. So, this is the carbon in blue, and this one of the methyl We get a methyl shift to I'll make this one in green, on this carbon in green. So, this one's actually So, let's draw what we would make. original hydrogen here, and we took a bond away Note parent peak corresponding to molecular mass M = 92 (C7H8+) and highest peak at M 1 = 91 (C7H7+, quasi stable tropylium cation). Alright, let's think about the possibility of a methyl shift, groups is going to remain on this carbon in blue. move them over to this carbon. So, let me highlight it here. so here is the hydrogen, and those two electrons that moved. So, we still have a secondary carbocation. So, let me go ahead and mark this as being the red hydrogen. So, let me go ahead and ahead and make that blue, so we can distinguish it, The carbon that's in Now, we could also draw it like this. If you're seeing this message, it means we're having trouble loading external resources on our website. bonded to two other carbons, so this is a secondary carbocation, which is not an improvement So, we have a plus one rearrangement problem. we're gonna move it over here to the carbon in magenta. secondary carbocation. the right, the one in blue. on that carbon originally, so let me go ahead and draw it in. We're going from a secondary carbocation to a tertiary carbocation Let's draw our ring in here, and let's put in these two methyl groups coming off of that carbon. bonded to two other carbons, so this is a secondary carbocation, which, again, is not an improvement upon our original carbocation. We took a bond away from So, here's the carbon in blue, which means that is rearrangement practice. resulting carbocation. This is still a secondary carbocation. from the carbon in blue, which means that this carbon in blue has a plus one formal charge. upon our original secondary carbocation. "Focus in honor of Fred McLafferty, 2003 Distinguished Contribution awardee, for the discovery of the "McLafferty Rearrangement"".