Reactions and Mechanisms

The Organic Chemistry Reaction and Mechanism Guide will help you understand more than 185 of the most common reactions encountered in undergraduate organic chemistry.

The guide covers all the necessary reactions from the beginning of Org 1 (Structure and Bonding) to the end of Org 2 (Amino Acids) and everything in-between (Stereochemistry, Alkene & Alkyne Reactions, SN1/SN2/E1/E2, Dienes, Alcohols, Aldehydes, and Ketones…).

Each of the reactions include  step-by-step explanations, reagents, mechanisms, multiple examples, nuances, special cases, and rules, as well as practice quizzes from real-world exams.

Anyone can access the reactions highlighted in red.

If you’d like to unlock unlimited access to all the reactions in the guide, check out The Master Organic Chemistry Membership, where you’ll also get full access to 1500+ organic chemistry practice quizzes from real-world exams, as well as 200+ printable flashcards that will help you identify and plug the gaps in your knowledge.

“The Reaction Guide was my key resource for exams. The concise, consistent format for each and every reaction I needed meant I could memorize reactions and spit them out on exams automatically. It worked, I surprised myself and got an A in Org 1.” -Kathleen N, City College, CUNY, NY.

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Comment section

53 thoughts on “Reactions and Mechanisms

  1. These rxn guides are not helping me with O chem 1. My professor has questions much harder than the flashcards with multiple steps can you help with this?

    Can you post common reactants and solvents associated with their most common reactions?

    Can you do a one page sheet that has rxn, mechanism, and clues that it is that rxn?

  2. Hi James! Just wanted to ask you why do we prefer dialkyl cadmium more than Grignard reagent to prepare ketone from acid chloride?

    1. Generally I would prefer dialkyl cuprate to dialkyl cadmium for conversion of an alkyl halide to a ketone, but dialkyl cadmium will also work. Both of these reagents will convert acid halides to ketones without addition to ketones. (see JACS 1972 vol 94 8593)

      One contributing factor to the high reactivity of Grignard reagents towards carbonyls is the Lewis acidic character of the magnesium, which coordinates to oxygen and activates the carbonyl carbon toward nucleophilic attack. This is much less of a problem with the less oxophilic metals copper and cadmium.

  3. If I consider a 3-bromo 1-cyclohexene will the bromine be on the plane or not?
    If not lets say its above the plane in that case if I brominate the cyclohexene for anti addition , among the added bromines which will be above the plane and which will be below .. because with respect to the 3- bromo .. both the structures would be different isn’t it ?…..

  4. If a compound containing a double bond and nitro-group is allowed to react with only 1 equivalent of Hydrogen using Nickel, then among double bond and nitro-group, which one will be reduced first??

    1. Is this a theoretical question or an actual transformation you are doing in a lab?

      For catalytic hydrogenation with Pd-C/H2, nitro is generally more easily reduced than a double bond. My reference is Pd-C in Paquette’s encyclopedia of reagents for organic synthesis, volume 6, available for loan (free) on

      It is possible to find conditions that will selectively reduce the alkene without reducing the nitro group. It is also possible to reduce a nitro group without affecting a double bond elsewhere in the molecule.

      Is the double bond conjugated to the nitro group, or is it isolated from the nitro group? Conjugation between the nitro and the double bond will make the alkene somewhat less likely to undergo catalytic hydrogenation.

  5. Hey James, awesome website you have here.
    I was wondering if you could shed some light on the use of Br2/H20 as an oxidising agent. My professor didn’t go into too much detail on it, but just said that it’s used to convert glucose to gluconic acid. I was wondering if there are any other uses of bromine water and if there was any mechanism to it.

    1. Hi, yes. Bromine and water can be used to oxidize aldehydes to carboxylic acids. What happens first is formation of a hydrate from water adding to the aldehyde.
      The next step is one of the oxygens of the hydrate attacks Br2 to form a new O-Br bond. You can think of this as putting a good “leaving group” on oxygen. The last step is that a weak base will break the C-H bond and essentially do an E2 type elimination reaction forming the C=O pi bond and breaking the O-Br bond.

      Most oxidations look pretty mysterious at first but when you look at the mechanism it’s essentially just a funky E2 with the leaving group on oxygen instead of carbon. Does that make sense?
      Demystifying oxidations:

  6. This site helped me to pass the organic chemistry exam. Thank you so much, you are doing a great work!

  7. Hi, I just subscribed for a membership, it’s great to have it all here!
    Just wanted to ask if you’ll add anything about pericyclic reactions? Thanks!

  8. Hey awesome site you have got here!!! Just a suggestion but my professor focuses in on a lot of the analytical portions of organic chemistry stuff like determining the type of carbohydrate from HIO4 (periodic acid cleavage) for carbohydrates?
    Or even a section on amino acids would be awesome, like determine the sequence of amino acids in a polypeptide or the Sanger reagent/reaction! Thank you for everything!!!

  9. This website is a really help to learn beginner teach chemesrtry and all type of material like reaction to teach in website

  10. Could you add the Simmons-Smith reaction to this guide? We went over it in my Orgo 2 class and I was a little confused. Thanks!

  11. I have found this site very very helpful at many points through my journey in Org 1 and 2, but now, towards the end of org 2 I am finding it less and less useful, which seems strange since there are more and more reactions. Why are there so few reactions of carboxylic acids? carboxylic acid chemistry is the core of org 2, not to mention biochemistry. It would be really really helpful if there were more of them. Also, I think there needs to be some consistency with where reactions are placed, if they are going from a type of molecule, they should all be grouped in that grouping, or maybe have two legends so reactions can be looked up based on their reactant or product.

    1. Not covered here. Although the mechanism is just the reverse reaction of alkene halogenation: formation of a 3 membered ring (halonium ion) followed by attack of the halonium X by a halide ion.

  12. Hi James,
    I have been poking around your site looking for some helpful tips on figuring out the most reactive site on a molecule. Our professor expects us to memorize pKa’s of about 20 different acids, but I just can’t make them stick. I know to use resonance, inductive, etc., arguments, but sometimes those seem ambiguous. Here is an example of where I should be able to easily decide how the reaction progresses, but I can’t decide whether to protonate the oxygen, or the c=c. Do you have any tips?
    Example: Show the reaction of 4,4-dimethylpent-1-en-3-one with H3O+.

    1. Well, that compound in particular is an α,β-unsaturated ketone AKA an enone. The hyperconjugation of the C=O and C=C bonds stabilizes this class of compounds enough that it gets a section in textbooks, but the ultimate takeaway is that the same reactions that occur for alkenes and ketones still happen for enones. If you look at James’s mechanisms for the enone reactions, you can see that they’re all 1,4-additions. This gives you the clue that the alkene is where any nucleophile is going to attack. In aqueous acid, H3O+ would protonate the alkene, and H2O would initiate nucleophilic attack on the resulting positive charge. As a side note: the extra methyl groups on the other side of the enone are there to make it clear that there are no competing reactions going on there, by eliminating alpha hydrogens.
      But what if you didn’t have a collection of mechanisms to reference? You can use the same factors that gauge acidity to determine that there’s a charge gradient from the terminal alkyne (δ+) to the O (δ-). Although the following post concerns acidity, the arguments you mentioned, resonance, etc. can be applied here too. They may seem ambiguous, but they do have a clear hierarchy for the most part. As always, beware of exceptions, though I don’t see any in the case of your enone.

      1. Thanks for your thoughtful reply. I have found lots of resources for reactions of alpha-beta unsaturated ketones, but all of the reactions require basic conditions. I think the purpose for this question is to find the starting materials for the aldol reaction. I will have to read up on the reactions involving alpha-beta unsaturated ketones.

        1. I don’t think this will lead to an aldol reaction because hyperconjugation stabilizes the carbonyl such that enones don’t undergo 1,2-addition in the presence of most nucleophiles. I think Grignard reagents are the most common exception, though.

  13. Hey all great stuff here. Was just curious, why no reduction of carbonyls via desulfurization? I see you have Wolff-Kisher and Clemmenson, why not the 3rd?

  14. Hey Jim,
    I have to teach grade 11 AP chem this term and forgot all my orgo from 30 yrs back. The site gave me a great kickstart.
    Spaseeba from Kazakhstan.
    Mr. J

  15. Hi James,
    Excellent contribution! But I wonder is there any pdf or somekind of print version which might help people use these reaction guide as flash cards or carry them?

  16. check the page source code, hydrate formation on aldehydes and ketones are redirected to addition of LiAlH4 on ketones

  17. Without your site I probably would not have gotten a B+ in Organic. I tell everybody to use your site. Hopefully I do better in organic 2. Thanks a million.

  18. This guide is great. One thing I was wondering though, would 1,2/1,4/1,6 addition to conjugated dienes go under reactions of alkenes and if so, do you think you’ll get around to posting that? Same for the Diels-Alder reaction. Thanks again, I greatly appreciate your efforts and passion for organic chemistry!

    1. thanks! I need to reorganize this page soon. If you look near the bottom, you’ll see a section on a,B-unsaturated ketones.

  19. I’m a “printer”. I find wonderful resources (and this is website is one of the best – it’s incredible) and print them and carry them with me to study like flashcards. I wonder if there might be a “view/print” option that allows you to see the name of the reaction (like you have above) with just a tidy concise example/mechanism below it. That way someone could print off, say, reactions of alcohols. They would have a super fast review on their hands. With of course, the option of logging back on to click the reaction and get more detailed information (as you have it set up now). But mostly, I just need a memory jogger now and then, or confirmation that yes, the intermediate is a carbocation and not an oxacyclopentane, or no, I haven’t lost my marbles and gotten a set of electron pushing arrows in the wrong spot. They do go indeed from such and such to such and such.
    Thank you!!!!!!!!!!!!!!!

    1. Thanks Jennifer – that’s something I’d like to do, just working for the moment on just getting the reactions up!

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