Draw the structure of the organic product for the reaction between the following compound and the phosphorus ylide shown.
Solution
The phosphorus ylide will only react with the carbonyl group.
Final product
Comment: Think of the Wittig reaction as the reverse of oxidative cleavage of alkenes.
Baeyer-Viliger Oxidation
The Baeyer-Viliger oxidation is an organic reaction used to convert a ketone to an ester using a peroxyacid, with an “insertion” of one oxygen atom.
• A peroxyacid can be prepared by reacting a carboxylic acid and hydrogen peroxide. RCOOH + H2O2 RCO3H + H2O
• Peroxyacids serve as the oxidizing agent in the Baeyer-Viliger reaction.
• For asymmetrical
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Carboxylic acids are stronger acids than peroxyacids.
The negative charge on the oxygen atom of the carboxylate ion is extensively delocalized between two highly electronegative oxygen atoms; thus the conjugate base is resonance stabilized. Furthermore, the presence of two highly electronegative oxygen atoms will also exert a strong electron withdrawing inductive effect, leading to a more effective dispersal of the negative charge on the oxygen atom of the carboxylate ion.
The negative charge on the conjugate base of the peroxyacid is not resonance stabilized. However, the presence of three highly electronegative oxygen atoms does exert a strong electron withdrawing inductive effect on the negative charge on the oxygen atom of the conjugate base. Nevertheless, the extent of negative charge dispersal is more effective for the carboxylate ion than for the conjugate base of a peroxyacid.
Example 1
The acid dissociation constants, Ka, of four compounds are shown as follows.
Explain the decreasing trend in acid strength of the four compounds.
compound Ka/ mol dm-3
2-hydroxybenzoic acid
1.1 x
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N.B.: R refers to an electron-donating alkyl group.
Aliphatic amines are more basic than phenylamines and phenylamines are more basic than amides.
For aliphatic amines, the more R groups present, the stronger is the electron donating inductive effect. Thus, a tertiary amine is expected to be the most basic among the aliphatic amines. However, it isn’t. A tertiary amine is less basic than a secondary amine despite the former having three electron donating alkyl groups as compared to the latter’s two. This is because although the electron donating inductive effect is greater for the tertiary amine, the presence of three ‘bulky’ alkyl groups hinders its ability to donate its lone pair of electrons. For this particular example, the steric factor is more dominant than the electronic factor.
For phenylamine, the lone pair of electrons on the N atom is delocalised in the benzene ring and hence renders them less available for coordination with a proton.
For amides, the lone pair of electrons on the N atom is delocalized into the adjacent carbonyl group with a highly electronegative oxygen atom. Hence, amides are considered to be
Wittig reactions allow the generation of an alkene from the reaction between an aldehyde/ketone and an alkyl halide (derived from phosphonium salt).The mechanism for the synthesis of trans-9-(2-phenylethenyl) anthracene first requires the formation of the phosphonium salt by the addition of triphenylphosphine and alkyl halide. The phosphonium halide is produced through the nucleophilic substitution of 1° and 2° alkyl halides and triphenylphosphine (the nucleophile and weak base). An example is benzyltriphenylphosphonium chloride, which was used in this experiment. The second step in the formation of the of the Wittig reagent, which is primarily called a ylide and derived from a phosphonium halide. In the formation of the ylide, the phosphonium ion in benzyltriphenylphosphonium chloride is deprotonated by the base, sodium hydroxide to produce the ylide as shown in equation 1.
Very strong oxidising agents would be needed to oxidise ketones. An example of an oxidising agent would be potassium manganate solution. When ketones are oxidised, the carbon-carbon bonds are broken. To reduce aldehydes and ketones, reducing agents would be used. Examples of reducing agents are, lithium tetrahydridoaluminate and sodium tetrahydridoborate.
Rasmussen, T.; Jensen, J. F.; Ostergaard, N.; Tanner, D.; Ziegler, T.; Norrby, P. Chem. Eur. J., 2002, 8, 177.
In this report we will discuss the rate in which catalase, a type of enzyme, reacts with hydrogen peroxide to create oxygen. We measured the rate that oxygen filled up a glass test tube filled with water, adding more catalase to the hydrogen peroxide to see if oxygen would be made faster.
At the time of conducting the experiment, the intention was to analyse the effect that an increase in catalase concentration had on the amount of oxygen (O2) produced if the hydrogen peroxide (H2O2) concentration was constant. It was proposed that when the catalase increases in concentration at the increments of 0.5%, 1%, 2%, and 4% and the hydrogen peroxide remained at a fixed concentration, the oxygen production would rise gradually. It was suggested that this would occur due to the collision theory ("BBC - GCSE Bitesize: Collision Theory") and the greater number of active sites thus an increase in accessibility allowing enzyme- substrate complex’s to be formed. According to the data gathered from the experiment, it can be implied that the hypothesis was supported as the data indicates an incline in oxygen
The tertiary product forms as a result of a hydride shift in order to form a more stable carbocation whereas the secondary (minor) product forms as a result of a direct substitution. The reaction was done via a hot water bath at approximately 55 degrees Celsius in order to overcome some of the activation energy requirements. The analysis of Infrared spectroscopy data showed that there was still a slight amount of alcohol left in the product therefore highlighting that this reaction did not go to completion. This could have been because of an excess of lucas
In this experiment it is only focused on substitution reactions. “In a substitution reaction, an electron-rich species donates a pair of electrons to an electron poor species which forms a new product and a new base” (2). There are multiple types off substitution reactions and they are
Propylhexedrine is a TAAE1 agonist and targets two known proteins synaptic vesicular amine transporter and trace amine-associated receptor 1. Synaptic vesicular amine transporter is a protein that is involved in the ATP-dependent vesicular transport of biogenic amine neurotransmitters. Trace amine-associated receptor 1 is a receptor for trace amines. The drugs main method is as an alpha beta-adrenoceptor agonist, which causes
The better leaving group is Bromine. From the SN1 reactions, all alkyl bromides, with the exception of Bromobenzene, produced precipitates at room temperature. Although only the first tube in the SN2 reactions produced precipitate at room temperature, the back side attack happened where expected. It is notable, that in the SN¬2 reaction, eventually all alkyl bromides produced precipitate still with the exception prior.
According to the principle of charge balance, there must be equal number of cationic and anionic (H+ and K+) species in the PBX solution. Fig. 5 show that the concentration of IC was maintained at 0 mg/L during the entire oxidation process, indicating that there is no CO32- and HCO3- in this solution. The ion
The water in the mixture acts as a nucleophile and the hydrolysis reaction occurs. During the hydrolysis reaction, halogenoalkanes are broken down in the presence of water to form alcohol, hydrogen ion and also halide
They are best performed in polar protic solvents such as ethanol, which allows for further stabilization of the carbocation. Steric hindrance has the opposite effect on SN1 reactions than SN2 reactions; the steric hindrance carbon chain helps stabilize the carbocation and results in a high inductive effect. This is in terms of the attraction of the nucleophile for the carbocation. The stabilization of the carbocation is exemplified by substrate 5 which reacted immediately in the presence of ethanolic silver nitrate solution. Although substrates 6 and 7 are primary halides, the allylic and benzylic nature allows the pi bonds to create a more stable environment for the surrounding carbocation allowing for a faster reaction.
(no date)). Ionic bonds can be affected by changes in charge. These ionic bonds contribute to the enzymes tertiary and quaternary structure. The proteins configuration and activity would thereby be changed (Rodillas et al. (no
Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory (VSEPR). VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy (i.e. most stable) structure for any bonding arrangement. In this way, VSEPR is a powerful tool for predicting the geometries of covalent molecules.
The aim of this investigation is to: 1) find the rate equation for the reaction between hydrogen peroxide, potassium iodide and sulphuric acid by using the iodine stop clock method and plotting graphs of 1/time against concentration for each variable. Then to find the activation energy by carrying out the experiment at different temperatures using constant amounts of each reactant and then by plotting a graph of in 1/t against I/T, 3) to deduce as much information about the mechanism as possible from the rate equation.