diabetestalk.net

Is An Aldehyde Or Ketone More Acidic?

Oxygen Containing Compounds - Aldehydes And Ketones

Oxygen Containing Compounds - Aldehydes And Ketones

Description nomenclature Aldehyde suffix: -al, -aldehyde. Ketone prefix: keto-, oxo-. Ketone suffix: -one, ketone. physical properties C=O bond is polar, with the carbon partially positive and oxygen partially negative. Dipole-dipole interactions give these molecules higher boiling points than their corresponding alkanes, but not as high as the corresponding alcohols or carboxylic acids. infrared absorption of C=O bond: 1700 cm-1 Important reactions nucleophilic addition reactions at C=O bond acetal, hemiacetal Aldehydes and ketones react with 1 equivalent of alcohols to make hemiacetals. Aldehydes and ketones react with 2 equivalent of alcohols to make acetals. Hemiketal and ketal are the same as acetals except the starting compound must be a ketone and not an aldehyde. This is an old naming scheme that is no longer used. imine, enamine Secondary amine + aldehyde or ketone = enamine. reactions at adjacent positions haloform reactions Ketones + halogen = halogenation of the alpha position (carbon adjacent to the C=O group). Methyl ketone + halogen = haloform + carboxylate. Trihalogenated methyl = good leaving group. aldol condensation 2 acetaldehyde -> aldo. Works for carbonyl compounds with an acidic alpha proton. oxidation: aldehydes oxidize to carboxylic acids. Ketones do not oxidize further. 1,3-dicarbonyls: internal H-bonding Also referred to as active methylene compounds. Tautomerism causes one of the carbonyls to switch to its enol form, which contains an -OH group that hydrogen bonds with the other carbonyl C=O group on the same molecule. This is called intramolecular (internal) hydrogen bonding. keto-enol tautomerism Enol form is the one with the alcohol. Keto form is the one with the ketone. Keto form is more stable, it is the predominant form. organometallic Continue reading >>

Polarity Of Organic Compounds

Polarity Of Organic Compounds

Polarity of Organic Compounds Principles of Polarity: The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive. In general, the presence of an oxygen is more polar than a nitrogen because oxygen is more electronegative than nitrogen. The combination of carbons and hydrogens as in hydrocarbons or in the hydrocarbon portion of a molecule with a functional group is always NON-POLAR. Summary of Polarity See below for the details. Polarity Ranking of the Functional Groups: (most polar first) Amide > Acid > Alcohol > Ketone ~ Aldehyde > Amine > Ester > Ether > Alkane An abbreviated list to know well is: Amide > Acid > Alcohol > Amine > Ether > Alkane Organic Functional Group Polarity and Electrostatic Potential: The molecular electrostatic potential is the potential energy of a proton at a particular location near a molecule. Negative electrostatic potential corresponds to: partial negative charges (colored in shades of red). Positive electrostatic potential corresponds to: partial positive charges (colored in shades of blue). Boiling Point Definition: In a liquid the molecules are packed closely together with many random movements possible as molecules slip past each other. As a liquid is heated, the temperature is increased. As the temperature increases, the kinetic energy increases which causes increasing molecular motion (vibrations and molecules slipping pas each other). Eventually the molecular motion becomes so intense that the forces of attraction between the molecules is disrupted to to the extent the molecules break free of the liquid and become a gas. At the temperature of the boiling point, the liquid turns into a gas. The m Continue reading >>

Carbonyl Alpha-substitution Reactions

Carbonyl Alpha-substitution Reactions

Alpha-substitution reactions occur at the position next to the carbonyl group, the α-position, and involve the substitution of an α hydrogen atom by an electrophile, E, through either an enol or enolate ion intermediate.[1] Alpha substitution scheme Reaction mechanism[edit] Because their double bonds are electron rich, enols behave as nucleophiles and react with electrophiles in much the same way that alkenes do. But because of resonance electron donation of a lonepair of electron s on the neighboring oxygen, enols are more electron- rich and correspondingly more reactive than alkenes. Notice in the following electrostatic potential map of ethenol (H2C=CHOH) how there is a substantial amount of electron density on the α carbon. When an alkene reacts with an electrophile, such as HCl, initial addition of H+ gives an intermediate cation and subsequent reaction with Cl− yields an addition product. When an enol reacts with an electrophile, however, only the initial addition step is the same. Instead of reacting with CI− to give an addition product, the intermediate cation loses the OH− proton to give an α-substituted carbonyl compound.[1]:845 Alpha-halogenation of aldehydes and ketones[edit] A particularly common α-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their α positions by reaction Cl2, Br2 or I2 in acidic solution. Bromine in acetic acid solvent is often used. Remarkably, ketone halogenation also occurs in biological systems, particularly in marine alga, where dibromoacetaldehyde, bromoacetone, 1, l,l -tribromoacetone, and other related compounds have been found. The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate.[1]:846 Acidity of alpha-hydro Continue reading >>

Enolate Formation From Ketones

Enolate Formation From Ketones

Voiceover: In order to see how to form enolate anions, and in this video we're just gonna look in more detail how to form enolate anions from ketones. And so the ketone we have here is acetone. To find our alpha carbon, we just look at the carbon next to our carbonyl carbon, so this could be an alpha carbon, and this could be an alpha carbon. Each one of those alpha carbons has three alpha protons, and so there's a total of six. I'm just gonna draw one in here, and this is the one that we're going to show being deprotonated here. So, the base that's going to deprotonate acetone, we're gonna use LDA, which is Lithium Diisopropyl Amide And, I could go ahead and draw in the Lithium here, so Li Plus, and then we see the two isopropyl groups like that, a negative one charge on our nitrogen. So this is a very strong base, it's also very bulky and sterically hindered. So you can think about a lone pair of electrons in the nitrogen, taking that proton, leaving these electrons behind on this carbon, so we can go ahead and draw the conjugate base here. We would have electrons on this carbon now, that's a carbanion, so let me go ahead and show those electrons, these electrons in here magenta, are gonna come off onto this carbon. And this carbon is a [carbanae] because remember there's also two other hydrogens attached to it. So that's what gives it a negative one formal charge here. We can draw our resonance structure, we can show these electrons in magenta moving in here, these electrons coming off onto our oxygen, so for our resonance structure we would show the negative charge is now on our oxygen, this would be a negative one formal charge like that now. So the electrons in magenta moved into here to form our double bond, and then we can show the electrons in here in the blue Continue reading >>

Chemistry Of Enolates And Enols – Acidity Of Alpha-hydrogens

Chemistry Of Enolates And Enols – Acidity Of Alpha-hydrogens

In the presence of carbonyl functional group, the alpha-hydrogens of a molecule exhibit acidity i.e. in the presence of a base they can be abstracted very easily to yield a carbanion. The acidity of the α-hydrogen of carbonyl compounds depends on the stability of the carbanion formed (which is the conjugate base in this case). If the carbanion is more stable, the alpha-hydrogen is more acidic. The carbanion can be stabilized either with resonance – i.e. the carbanion lone pair to the oxygen of the carbonyl to form the stabilized enolate, or by inductive effect – if electron withdrawing groups are directly attached to the alpha-carbon. Stabilization by inductive effect - if electron withdrawing groups are directly attached to the alpha-carbon. Note – Acidities of the alpha-hydrogen is measured in pKa. Lower pKa value of the hydrogen, more acidic it is. Comparison of Acidities of Alpha – Hydrogens Note – The pKa values are given assuming the R’ and R” groups are alkyl (mostly methyl group) and are an approximate value. 1] α-Hydrogens of Ketones vs Aldehydes The alpha-hydrogens of ketones (pKa = 20) are less acidic as compared to aldehydes (pKa = 17). This is because the alkyl group R” of ketones pushes electrons via inductive effect on to the alpha-carbon. This would increase the electron density at the alpha-carbon to slightly destabilize the formation of the conjugate base – carbanion. 2] α-Hydrogens of Ketones vs Esters The alpha-hydrogen of ketones (pKa = 20) is more acidic as compared to the alpha-hydrogens of esters (pKa = 25). The reason for this is that the ester functional group has free lone pairs on the oxygen which can participate in resonance with carbonyl group. This resonance competes with the resonance of the stabilization of the enola Continue reading >>

Like This Study Set?

Like This Study Set?

Sort How can you form one product with a crossed aldol addition reaction using LDA? (18.12) If both aldehydes have α-hydrogens. LDA used to remove the α-hydrogens that creates the enolate ion. (LDA is a strong base- all carbonyl compound converted to an enolate so none of the carbonyl compound will be left for the enolate ion to react with an aldol addition) Aldol addition cannot occur until the second carbonyl compound is added slowly (minimize chance that aldehyde w/ α-hydrogen forming an enolate ion and reacting with it parent compound) Continue reading >>

Acidity Of

Acidity Of

Acidity of a-Hydrogens In the following table, the acidity of the H for various enolate systems and other closely related systems are given. You should be able to justify the trends in this data ! Why are the protons adjacent to carbonyl groups acidic ? As we have advocated before, look at the stabilization of the conjugate base. Notice the proximity of the adjacent p system, and hence the possibility for RESONANCE stabilization by delocalisation of the negative charge to the more electronegative oxygen atom. The more effective the resonance stabilization of the negative charge, the more stable the conjugate base is and therefore the more acidic the parent system. Let's compare pKa of the common systems: aldehyde pKa = 17, ketone pKa = 19 and an ester pKa = 25, and try to justify the trend. The difference between the 3 systems is in the nature of the group attached to the common carbonyl. The aldehyde has a hydrogen, the ketone an alkyl- group and the ester an alkoxy- group. H atoms are regarded as having no electronic effect : they don't withdraw or donate electrons. Alkyl groups are weakly electron donating, they tend to destabilize anions (you should recall that they stabilize carbocations). This is because they will be "pushing" electrons towards a negative system which is unfavourable electrostatically. Hence, the anion of a ketone, where there are extra alkyl groups is less stable than that of an aldehyde, and so, a ketone is less acidic. In the ester, there is also a resonance donation from the alkoxy group towards the carbonyl that competes with the stabilization of the enolate charge. This makes the ester enolate less stable than those of aldehydes and ketones so esters are even less acidic. The most important reactions of ester enolates are the Claisen and Die Continue reading >>

Carbonyl Functional Groups

Carbonyl Functional Groups

Chapter 15 - Carbonyl Compounds usually subdivided into two families: aldehydes and ketones both R groups are C or H carboxyl derivatives X is some electronegative element (halogen, O, N, S, others) The Carbonyl Group - Structure and Properties polar C=O double bond O is nucleophilic reacts with acids & electrophiles C is electrophilic reacts with Lewis bases and nucleophiles alpha-C-H position is acidic (pKa ~ 20) Aldehyde Nomenclature IUPAC: alkanal -al suffix, with carbonyl assumed #1 in parent chain -carbaldehyde suffix (if aldehyde can't be part of the parent) e.g., cyclohexanecarbaldehyde common nomenclature: formaldehyde acetaldehyde propionaldehyde butyraldehyde benzaldehyde Ketone Nomenclature IUPAC: alkanone -one suffix, with number -oxo- prefix if necessary e.g., 4-oxopentanal common nomenclature: dialkyl ketone acetone acetophenone benzophenone acyl- as prefix e.g., acetyl or benzoyl, as in acetylcyclopropane Precedence Order of Functional Groups decides which gets to be the parent compound (suffix) lower functional groups must be named as substituents (prefixes) carboxylic acid aldehyde ketone alcohol amine thiol Characteristic Properties polar H-bond acceptors, but not H-bond donors Mass spec shows alpha cleavage (stable acylium ion RCO+) or McLafferty rearrangement (split between alpha and beta carbons) NMR shows aldehyde C-H at 9-10 ppm, C=O at 180-210 ppm IR shows strong C=O stretch at 1600-1800 cm-1 exact position depends on ring strain, conjugation UV shows weak n -> pi* at ~ 300 nm and pi -> pi* at ~ 200 nm exact position and strength of the absorption depends on conjugation Nucleophilic Addition to Carbonyls the major reaction of carbonyl compounds General Trends: aldehydes more reactive than ketones (due to steric hindrance with ketones) aromatic c Continue reading >>

18.1: Acidity Of Aldehydes And Ketones: Enolate Ions

18.1: Acidity Of Aldehydes And Ketones: Enolate Ions

For alkylation reactions of enolate anions to be useful, these intermediates must be generated in high concentration in the absence of other strong nucleophiles and bases. The aqueous base conditions used for the aldol condensation are not suitable because the enolate anions of simple carbonyl compounds are formed in very low concentration, and hydroxide or alkoxide bases induce competing SN2 and E2 reactions of alkyl halides. It is necessary, therefore, to achieve complete conversion of aldehyde or ketone reactants to their enolate conjugate bases by treatment with a very strong base (pKa > 25) in a non-hydroxylic solvent before any alkyl halides are added to the reaction system. Some bases that have been used for enolate anion formation are: NaH (sodium hydride, pKa > 45), NaNH2 (sodium amide, pKa = 34), and LiN[CH(CH3)2]2 (lithium diisopropylamide, LDA, pKa 36). Ether solvents like tetrahydrofuran (THF) are commonly used for enolate anion formation. With the exception of sodium hydride and sodium amide, most of these bases are soluble in THF. Certain other strong bases, such as alkyl lithium and Grignard reagents, cannot be used to make enolate anions because they rapidly and irreversibly add to carbonyl groups. Nevertheless, these very strong bases are useful in making soluble amide bases. In the preparation of lithium diisopropylamide (LDA), for example, the only other product is the gaseous alkane butane. Because of its solubility in THF, LDA is a widely used base for enolate anion formation. In this application, one equivalent of diisopropylamine is produced along with the lithium enolate, but this normally does not interfere with the enolate reactions and is easily removed from the products by washing with aqueous acid. Although the reaction of carbonyl compound Continue reading >>

Functional Group Names, Properties, And Reactions

Functional Group Names, Properties, And Reactions

Functional Groups Functional groups refer to specific atoms bonded in a certain arrangement that give a compound certain physical and chemical properties. Learning Objectives Define the term “functional group” as it applies to organic molecules Key Takeaways Functional groups are often used to “functionalize” a compound, affording it different physical and chemical properties than it would have in its original form. Functional groups will undergo the same type of reactions regardless of the compound of which they are a part; however, the presence of certain functional groups within close proximity can limit reactivity. Functional groups can be used to distinguish similar compounds from each other. functional group: A specific grouping of elements that is characteristic of a class of compounds, and determines some properties and reactions of that class. functionalization: Addition of specific functional groups to afford the compound new, desirable properties. The Role of Functional Groups In organic chemistry, a functional group is a specific group of atoms or bonds within a compound that is responsible for the characteristic chemical reactions of that compound. The same functional group will behave in a similar fashion, by undergoing similar reactions, regardless of the compound of which it is a part. Functional groups also play an important part in organic compound nomenclature; combining the names of the functional groups with the names of the parent alkanes provides a way to distinguish compounds. The atoms of a functional group are linked together and to the rest of the compound by covalent bonds. The first carbon atom that attaches to the functional group is referred to as the alpha carbon; the second, the beta carbon; the third, the gamma carbon, etc. Simi Continue reading >>

Reactions Of Aldehydes And Ketones

Reactions Of Aldehydes And Ketones

Aldehydes and ketones undergo a variety of reactions that lead to many different products. The most common reactions are nucleophilic addition reactions, which lead to the formation of alcohols, alkenes, diols, cyanohydrins (RCH(OH)C&tbond;N), and imines R 2C&dbond;NR), to mention a few representative examples. The main reactions of the carbonyl group are nucleophilic additions to the carbon‐oxygen double bond. As shown below, this addition consists of adding a nucleophile and a hydrogen across the carbon‐oxygen double bond. Due to differences in electronegativities, the carbonyl group is polarized. The carbon atom has a partial positive charge, and the oxygen atom has a partially negative charge. Aldehydes are usually more reactive toward nucleophilic substitutions than ketones because of both steric and electronic effects. In aldehydes, the relatively small hydrogen atom is attached to one side of the carbonyl group, while a larger R group is affixed to the other side. In ketones, however, R groups are attached to both sides of the carbonyl group. Thus, steric hindrance is less in aldehydes than in ketones. Electronically, aldehydes have only one R group to supply electrons toward the partially positive carbonyl carbon, while ketones have two electron‐supplying groups attached to the carbonyl carbon. The greater amount of electrons being supplied to the carbonyl carbon, the less the partial positive charge on this atom and the weaker it will become as a nucleus. The addition of water to an aldehyde results in the formation of a hydrate. The formation of a hydrate proceeds via a nucleophilic addition mechanism. 1. Water, acting as a nucleophile, is attracted to the partially positive carbon of the carbonyl group, generating an oxonium ion. Acetal formation reacti Continue reading >>

Acidity Of

Acidity Of

a-Hydrogens In the following table, the acidity of the H for various enolate systems and other closely related systems are given. You should be able to justify the trends in this data ! Why are the protons adjacent to carbonyl groups acidic ? As we have advocated before, look at the stabilisation of the conjugate base. Notice the proximity of the adjacent p system, and hence the possibility for RESONANCE stabilisation by delocalisation of the negative charge to the more electronegative oxygen atom. The more effective the resonance stabilisation of the negative charge, the more stable the conjugate base is and therefore the more acidic the parent system. Let's compare pKa of the common systems: aldehyde pKa = 17, ketone pKa = 19 and an ester pKa = 25, and try to justify the trend. The difference between the 3 systems is in the nature of the group attached to the common carbonyl. The aldehyde has a hydrogen, the ketone an alkyl- group and the ester an alkoxy- group. H atoms are regarded as having no electronic effect : they don't withdraw or donate electrons. Alkyl groups are weakly electron donating, they tend to destabilise anions (you should recall that they stabilise carbocations). This is because they will be "pushing" electrons towards a negative system which is unfavourable electrostatically. Hence, the anion of a ketone, where there are extra alkyl groups is less stable than that of an aldehyde, and so, a ketone is less acidic. In the ester, there is also a resonance donation from the alkoxy group towards the carbonyl that competes with the stabilisation of the enolate charge. This makes the ester enolate less stable than those of aldehydes and ketones so esters are even less acidic. The most important reactions of ester enolates are the Claisen and Dieckmann cond Continue reading >>

Organic Chemistry/ketones And Aldehydes

Organic Chemistry/ketones And Aldehydes

Aldehydes () and ketones () are both carbonyl compounds. They are organic compounds in which the carbonyl carbon is connected to C or H atoms on either side. An aldehyde has one or both vacancies of the carbonyl carbon satisfied by a H atom, while a ketone has both its vacancies satisfied by carbon. 3 Preparing Aldehydes and Ketones Ketones are named by replacing the -e in the alkane name with -one. The carbon chain is numbered so that the ketone carbon, called the carbonyl group, gets the lowest number. For example, would be named 2-butanone because the root structure is butane and the ketone group is on the number two carbon. Alternatively, functional class nomenclature of ketones is also recognized by IUPAC, which is done by naming the substituents attached to the carbonyl group in alphabetical order, ending with the word ketone. The above example of 2-butanone can also be named ethyl methyl ketone using this method. If two ketone groups are on the same structure, the ending -dione would be added to the alkane name, such as heptane-2,5-dione. Aldehydes replace the -e ending of an alkane with -al for an aldehyde. Since an aldehyde is always at the carbon that is numbered one, a number designation is not needed. For example, the aldehyde of pentane would simply be pentanal. The -CH=O group of aldehydes is known as a formyl group. When a formyl group is attached to a ring, the ring name is followed by the suffix "carbaldehyde". For example, a hexane ring with a formyl group is named cyclohexanecarbaldehyde. Aldehyde and ketone polarity is characterized by the high dipole moments of their carbonyl group, which makes them rather polar molecules. They are more polar than alkenes and ethers, though because they lack hydrogen, they cannot participate in hydrogen bonding like Continue reading >>

Acidity Of Alpha Hydrogens & Keto-enol Tautomerism

Acidity Of Alpha Hydrogens & Keto-enol Tautomerism

Alkyl hydrogen atoms bonded to a carbon atom in a a (alpha) position relative to a carbonyl group display unusual acidity. While the pKa values for alkyl C-H bonds is typically on the order of 40-50, pKa values for these alpha hydrogens is more on the order of 19-20. This can most easily be explained by resonance stabilization of the product carbanion, as illustrated in the diagram below. In the presence of a proton source, the product can either revert back into the starting ketone or aldehyde or can form a new product, the enol. The equilibrium reaction between the ketone or aldehyde and the enol form is commonly referred to as "keto-enol tautomerism". The ketone or aldehyde is generally strongly favored in this reaction. Because carbonyl groups are sp2 hybridized the carbon and oxygen both have unhybridized p orbitals which can overlap to form the C=O bond. The presence of these overlapping p orbitals gives hydrogens (Hydrogens on carbons adjacent to carbonyls) special properties. In particular, hydrogens are weakly acidic because the conjugate base, called an enolate, is stabilized though conjugation with the orbitals of the carbonyl. The effect of the carbonyl is seen when comparing the pKa for the hydrogens of aldehydes (~16-18), ketones (~19-21), and esters (~23-25) to the pKa of an alkane (~50). Of the two resonance structures of the enolate ion the one which places the negative charge on the oxygen is the most stable. This is because the negative change will be better stabilized by the greater electronegativity of the oxygen. Keto-enol Tautomerism Because of the acidity of α hydrogens carbonyls undergo keto-enol tautomerism. Tautomers are rapidly interconverted constitutional isomers, usually distinguished by a different bonding location for a labile hydrogen Continue reading >>

Why Are Aldehydes And Ketones Neutral And Not Acidic/basic?

Why Are Aldehydes And Ketones Neutral And Not Acidic/basic?

This question is quite general, and as other answers have pointed out, depends on what you mean by acidic/basic. The other answers have already covered the Lewis bit, so I will focus a bit more on the Bronsted-Lowry and Arrhenius definitions. In water, almost all aldehydes and ketones do not dissociate to give the H+ or OH- ion, which is the Arrhenius definition. However, the alpha position of acetylacetone is considered acidic by the Bronsted-Lowry definition, and can be deprotonated by strong bases to give the conjugated enone after tautomerism. This is due to the stability of the conjugate base. Continue reading >>

More in ketosis