What is Reaction mechanism: Definition and 25 Discussions

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each.

The electron or arrow pushing method is often used in illustrating a reaction mechanism; for example, see the illustration of the mechanism for benzoin condensation in the following examples section.
A reaction mechanism must also account for the order in which molecules react. Often what appears to be a single-step conversion is in fact a multistep reaction.

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  1. I

    Chemistry Reaction Mechanism of Cl2 and CHCl3

    I think the answer is both A) Cl and B) CCl3, since both are produced and used up. The correct solution is only A). Could anyone explain why? Thanks.
  2. HighFive5

    Chemistry Reaction Mechanism for Amide Formation: Do You Agree?

    Hello all! I wrote a reaction mechanism for a sequence that forms an amide. Do you agree with my answer? Thanks for your help!
  3. C

    Nuclear Reaction - How to determine variables as much as possible

    Hey Guys, exercise: "It is desired to study the first excited state of 16O which is at energy of 6.049 MeV. Using the (alpha, n) reaction on target of 13C, what is the minimum energy of incident alphas which will populate the excited state? So, i suggest to define first the reaction equation...
  4. J

    Flux-flux correlation function under Feynman's path integral

    This is a chemically inspired problem, but the path is fully quantum mechanics and a bunch of integrals. How does one calculate fully quantum mechanical rate ($\kappa$) in the golden-rule approximation for two linear potential energy surfaces? Attempt: Miller (83) proposes...
  5. Evangeline101

    Proposing a reaction mechanism

    1. Homework Statement 2. Homework Equations rate law equation 3. The Attempt at a Solution a) I would expect this reaction to be a multi-step reaction because there are six reactant molecules, as shown in the overall chemical equation. For this reaction to be one-step, all six molecules...
  6. ReidMerrill

    Organic reaction mechanism help -- Looking for resources

    I have an assignment in which I must find a named reaction, the original reference to it, and show what experimental evidence was used to develop the reactions mechanism. So far I've had no luck finding anything. It's hard enough finding the original reference and so far I haven't been able to...
  7. I

    Can't find this exact reaction mechanism online -- Help please....

    Homework Statement Homework EquationsThe Attempt at a Solution Can't find this exact reaction mechanism online. Help? http://imgur.com/a/X9P7e I don't know what the mild oxidation does. Does it split the double bond into a ketone and aldehyde?
  8. V

    Dehydration Problem: Solving for the Location of a Double Bond in a Carbocation

    Homework Statement Please see question number 31 http://cms.fiitjee.co/Resources/DownloadCentre/Document_Pdf_183.pdf Homework Equations none The Attempt at a Solution i got up to second step in the solution(scroll downwards) but in the last step a carbocation is formed and double bond can...
  9. B

    Reaction mechanism for ketone and vinyl lithium

    Homework Statement What is the product of 1-bromo-3-propanone treated with vinyl lithium? Homework EquationsThe Attempt at a Solution I know that the carbonyl is attcked by the organolithium but I am having a hard time understanding how it attaches to the carbonyl since it is sp2 hybridized...
  10. Mike Dacre

    NBS vs radical HBr in the bromination of olefins

    I am having some trouble understanding why different sources of bromine radicals supposedly brominate an alkene at different positions. What I mean by this: In the first example, the Bromine radical attacks a hydrogen at the allylic position and then a termination reaction results in a Bromine...
  11. N

    What is the Wittig reaction mechanism?

    Can anyone please walk me through the mechanism as this question does not make sense to me. I do have some understanding of the general mechanism. The answer is B) but I don't understand how to get there. The confusing aspect to me, is the structure of the ylide.
  12. B

    M-nitroacetophenone to m-aminoacetophenone reaction mechanism.

    I have this reaction mechanism but I am not sure if its correct or not. In lab we reduced the m-nitroacetophenone using tin and HCl and then using sodium hydroxide to make m-aminoacetophenone. This mechanism goes beyond the scope of our class and not sure why our lab teacher had us do it and its...
  13. A

    Ketosis/Ketoacidosis Reaction Mechanism?

    I'm in a first year organic chemistry class with a biochem focus and I am going to do a project on ketoacidosis. While I can find the pathway online, since this is an organic chemistry class, I figure that a reaction mechanism that illustrates electron movement (arrows and such) would be...
  14. K

    Reaction Mechanism Predictions

    A chemical Reaction A-->B is carried out in a closed vessel. The following data are taken for the concentration of A, Ca (g/L), as a function of time, t(min), from the start of the reaction. A proposed reaction mechanism predicts that Ca and t should be related by the expression ln...
  15. D

    Some help on correlating the reaction mechanism with the rate law

    Homework Statement Consider the following mechanism: (1) ClO^{-} (aq) + H2O (l) \Leftrightarrow HClO (aq) + OH^{-} (aq) [fast] (2) I^{-} (aq) + HClO (aq) \rightarrow HIO (aq) + Cl^{-} (aq) [slow] (3) OH^{-} (aq) + HIO (aq) \rightarrow H2O (l) + IO^{-} (aq) [fast] Is the mechanism...
  16. J

    Rate Law for IBr Decomposition: Explained Step-by-Step

    Write the rate law for the following proposed mechanism for the decomposition of IBr to I2 and Br2. IBr(g)---------->I(g) + Br(g) (fast) IBr(g) + Br(g)-------->I(g) + Br2(g) (slow) I(g) + I(g)--------->I2(g) (fast) The answer is R=k[IBr]^2. I don't know where this answer comes...
  17. T

    Chemical Kinetics: Reaction Mechanism (My working attempt shown)

    Homework Statement 1. According to the mechanism below, what is the correct expression for the rate of consumption of A? In the mechanism, M is a molecule that collides with A and A* is a highly-energized form of A. Step 1 (reversible): A + M <---> A* + M rate constants k1 and k-1 Step...
  18. T

    Chemical Kinetics: Reaction Mechanism

    Homework Statement 1. According to the mechanism below, what is the correct expression for the rate of consumption of A? In the mechanism, M is a molecule that collides with A and A* is a highly-energized form of A. Step 1 (reversible): A + M <---> A* + M rate constants k1 and k-1 Step...
  19. P

    Chemistry - Reaction Mechanism

    Homework Statement "Given the rate law for the following equation is Rate = k[A][B2] 2A + B2 ------> 2AB Suggest a mechanism for the reaction Homework Equations I have no clue; I was absent for 2 weeks and now have to teach myself the first two units, I've been...
  20. T

    What Is the Correct Rate Law for These Reaction Mechanisms?

    1. For the reaction 2NO + Cl2 --> 2NOCl Match the appropriate rate law to each postulated mechanism. A Rate = k[NO]2[Cl2]2 B Rate = k[NO][Cl2] C Rate = k[NO][Cl2]2 D Rate = k[Cl2] E Rate = k[Cl2]2 F Rate = k[NO] G Rate = k[NO]2[Cl2] H Rate = k[NO]2 I None of the...
  21. W

    Reaction Mechanism (Shouldn't Be Too Difficult)

    [SOLVED] Reaction Mechanism (Shouldn't Be Too Difficult) Homework Statement Write the equation for the overall reaction and identify any reaction intermediates: STEP 1: Cl2---> Cl + Cl STEP 2: Cl + CO---> COCl STEP 3: COCl + Cl2---> COCl2 + Cl Homework Equations See...
  22. A

    How Do Curly Arrows Illustrate Electron Movement in Acid Rain Formation?

    Homework Statement I have been working at this for about two days now and haven't really gotten any further. Unfortunately my teacher is away but last time he checked it over he said I was 'almost there' so a few extra nudges in the right direction would be appreciated! I'm trying to write...
  23. A

    Ground Level Ozone Production: Reaction Mechanism

    Hi, I need help with the following question: What are mechanisms of reactions that lead to the production of ground level ozone the chemical reaction is sunlight + VOCs + NOx -> Smog and Ozone can someone tell me waht the mechanism is or how to develope the mechanism
  24. D

    Reaction Rate of 4HCl + 4NaS2O3 -> Effects on Reaction

    I experimentally determined the reaction rate of the following reaction: 4HCl(aq) + 4NaS2O3(aq) -> 4NaCl(aq) + 3S(s) + 5SO2(aq) + 2H2O(l) and found that the rate was proportional to [NaS2O3]^1 and [HCl]^2 I know that it's probably too tricky to determine the reaction mechanism or rate...
  25. 2

    Why did the red color fade in the reaction between substance x(2+) and y(2+)?

    Year 11 chemistry problem the whole class is stuck on and our regular teacher is away for a month: A strip of substance x(2+) is placed in a red solution of y(2+) (aq). After 3 hours the red colour becomes less intense. There is no change after this. Some x(2+) still remains. a) write a...