limiting reagent

Examples of limiting reagent in the following topics:

• Limiting Reagents

  • The reagent that limits how much product is produced (the reactant that runs out first) is known as the limiting reagent.
  • If the amount of B present is less than is required, then B is the limiting reagent.
  • Since there is only 0.28 mol C2H3Br3 present, C2H3Br3 is the limiting reagent.
  • The reactant that produces the least amount of product is the limiting reagent.
  • Determine the limiting reagent and the amount of a product formed in a given reavion

• Calculating Theoretical and Percent Yield

  • A reaction should theoretically produce as much of the product as the stoichiometric ratio of product to the limiting reagent suggests.
  • The theoretical yield of a reaction is 100 percent, but this value becomes nearly impossible to achieve due to limitations.
  • Next, identify the limiting reagent.
  • This video explains the concept of a limiting reactant (or a limiting reagent) in a chemical reaction.
  • It also shows how to calculate the limiting reactant and the percent yield in a chemical reaction.

• Functionalized Organometallic Reagents

  • However, the reactivity of these powerful nucleophiles limits the functional groups that are tolerated in their preparation and use.
  • The first example is a conjugate addition of the mixed zinc-copper reagent to an unsaturated nitro compound.
  • Finally, the allylzinc reagent in equation #(ii) rearranges in the course of the coupling.
  • This brief discussion of functionalized organometallic reagents would not be complete without illustrating the synthetic utility of low temperature magnesium-halogen exchange reactions involving simple Grignard reagents.
  • The second example is more complex, and over a sequence of half a dozen steps, both aryl iodides are converted to Grignard reagents which are then converted to copper reagents prior to coupling reactions with alkyl halides.

• Amplifying DNA: The Polymerase Chain Reaction

  • The reaction produces a limited amount of final amplified product that is governed by the available reagents in the reaction, and the feedback-inhibition of the reaction products.
  • A basic PCR set up requires the following components and reagents:
  • Under optimum conditions (i.e., if there are no limitations due to limiting substrates or reagents) at each extension step, the amount of DNA target is doubled, leading to exponential (geometric) amplification of the specific DNA fragment.

• Organometallic Reagents from Geminal Dihalides

  • Lombardo's reagent, and several similar organotitanium compounds (e.g.
  • Tebbe's reagent) act to methylenate carbonyl groups.
  • In this sense they mimic Wittig reagents.
  • Because they are less basic than the alkylidenenephosphorane Wittig reagents, Lombardo reagents do not epimerize sensitive ketones, such as used in reaction (ii).
  • By converting these lithium reagents to Gilman (cuprate) reagents, conjugate addition to enones may be accomplished.

• Reactions with Organometallic Reagents

  • The facile addition of alkyl lithium reagents and Grignard reagents to aldehydes and ketones has been described.
  • The aldehyde or ketone product of this elimination then adds a second equivalent of the reagent.
  • The acidity of carboxylic acids and 1º & 2º-amides acts to convert Grignard and alkyl lithium reagents to hydrocarbons (see equations), so these functional groups should be avoided when these reagents are used.
  • Two such modifications that have proven effective are the Gilman reagent (R2CuLi) and organocadmium reagents (prepared in the manner shown).
  • Imines themselves do not react with Grignard reagents.

• Reactants and Reagents

  • In contrast, both alkyl bromides form Grignard reagents (RMgBr) on reaction with magnesium.
  • Apparently minor changes in a reagent may lead to a significant change in the course of a reaction.

• Important Reagent Bases

  • The significance of all these acid-base relationships to practical organic chemistry lies in the need for organic bases of varying strength, as reagents tailored to the requirements of specific reactions.
  • The common base sodium hydroxide is not soluble in many organic solvents, and is therefore not widely used as a reagent in organic reactions.
  • Most base reagents are alkoxide salts, amines or amide salts.

• Reactions of Substituent Groups

  • The reaction of alkyl and aryl halides with reactive metals (usually Li & Mg) to give nucleophilic reagents has been noted.
  • Many reactions of these aryl lithium and Grignard reagents will be discussed in later sections, and the following equations provide typical examples of carboxylation, protonation and Gilman coupling.
  • Just as an expert carpenter must understand the characteristics and limitations of his/her tools, chemists must appreciate the nature of their "tools" when applying them to a specific synthesis.

• Multiplex and Real-Time PCR

  • The starting material is a messenger RNA (mRNA) of interest that could be obtained from a wide array of sample types and extracted using commercially available kits and reagents.
  • Up to 20 different reactions can be run simultaneously, therefore lowering the amount of sample used, reducing the reagents consumed, and collecting far more information per reaction, while simplifying data analyses.
  • The key to successful multiplex PCR is the ability to define a single set of reaction parameters (reagent concentrations and cycling parameters) that allows for all primers to anneal with high specificity to their target sequences and be extended with the same efficiency.
  • It is evident that due to the limited number of fluorophoric labels available and the significant overlap in their emission spectra, quantification of multiplex reaction products is often difficult.