Organic Chemistry Aldehydes and Ketones

Question 1

___ are compounds that contain the carbonyl group, C||O, a double bond between a carbon atom and an oxygen atom. A ketone has two alkyl or aryl groups bonded to the carbonyl, placing the carbonyl group in the middle of the molecule. An aldehyde has one alkyl group and one hydrogen (or, in the case of formaldehyde, two hydrogens) bonded to the carbonyl; thus, an aldehyde is always found at the end of a molecule. Functional groups found at the end of a molecule are often called terminal groups
The carbonyl group is one of the most important functional groups in organic chemistry in large part because it possesses a dipole moment: the carbon carries a partial positive charge, and the oxygen carries a partial negative charge. In addition to its presence in aldehydes and ketones, it is also found in carboxylic acids, esters, amides, and more complicated compounds

Answer 1

aldehydes and ketones

Question 2

Because of their high degree of ___, aldehydes and ketones are usually the priority group in naming compounds. Note that the shorthand for an aldehyde group is always written -CHO; this should not b confused with the shorthand for an alcohol, which is C-OH. In the IUPAC system, molecules containing an aldehyde as the most oxidized group are named with suffix -al. The position of such an aldehyde group does not need to be specified: it must occupy the terminal (C-1) position. Common names exist for the first five aldehydes: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and valeraldehyde

Answer 2

oxidation

Question 3

In more complicated molecules, the suffix -carbaldehyde can be used. In addition, the ___ can be named as a functional group with the prefix formyl- when combined in a molecule with an even higher priority carboxylic acid group

Answer 3

aldehyde

Question 4

___ are named with the suffix -one. The location of the carbonyl group must be specified with a number, except in cyclic ketones, where it is assumed to occupy the number 1 position. The common system of naming ketones lists the two alkyl groups followed by the word ketone. When it is necessary to name the carbonyl as a substituent, the prefix oxo- is used.

Answer 4

ketones

Question 5

The physical properties of ___ are governed by the presence of the carbonyl group and its strong dipole moment. Due to differences in electronegativity, the carbon carries a strong partial positive charge, and the oxygen carries a strong partial negative charge. The dipole moments associated with the polar carbonyl groups of nearby molecules align, causing an elevation in boiling point of aldehydes and ketones relative to similar alkanes, However, aldehydes and ketones show lower boiling points than comparable alcohols because -OH groups can form hydrogen bonds, but carbonyls cannot

Answer 5

aldehydes and ketones

Question 6

There are three method of preparing ___ and ketones that are of interest: oxidation of alcohols, oxidative cleavage of alkenes, and Friedel-Crafts acylation of benzenes.
Th reactions of aldehydes and ketones are likewise interrelated with those of other compounds and are often driven by the dipole moment of the carbon-oxygen double bond. Aldehydes and ketones can be oxidized or reduced to form carboxylic acids or alcohols, respectively. They can act as either the nucleophile or substrate in SN1 and SN2-type reactions. They can serve as the substrate for nucleophilic attack on the carbonyl to produce alcohols, ethers, amides, and related compounds. Thy can condense to form larger molecules and to create double bonds.

Answer 6

aldehydes

Question 7

An ___ can be obtained from the oxidation of a primary alcohol; a ketone can be obtained from a secondary alcohol. these reactions are usually performed with PCC (one of the only options to create an aldehyde), potassium permanganate, sodium or Potassium dichromate, or chromium trioxide (Jones reagent).

Answer 7

aldehyde

Question 8

Ketones can also be synthesized by the cleavage of disubstituted alkenes with potassium ___

Answer 8

permanganate

Question 9

A reaction produces ___ of the form R-Co-Ar from benzene and an acyl halide in the presence of a Lewis acid such as AlCl3

Answer 9

ketones

Question 10

___ occupy the middle of the oxidation-reduction continuum. they are more oxidized than alcohols but less oxidized than carboxylic acids. Aldehydes can be oxidized with a number of different reagents, such as KMnO4, K2Cr2O7, CrO3, Ag2O (Tollen’s reagent), or H2O2. The product of oxidation of an aldehyde is a carboxylic acid. Ketones cannot undergo further oxidation unless extraordinarily harsh conditions are used to break C-C bonds. A number of different reagents will reduce aldehydes and ketones to alcohols. The two most common are lithium aluminum hydride (LAH), which is a stronger reducing agent, and sodium borohydride (NaBH4), which is milder; both, however, are effective on aldehydes and ketones

Answer 10

aldehydes and ketones

Question 11

Aldehydes and ketones can be completely reduced to alkanes by two common methods. In the Wolff-Kishner reduction, the ___ is first converted to a hydrazone, which then releases molecular nitrogen (N2) when heated and forms an alkane. The Wolff-Kishner reaction is performed in basic solution and therefore is only useful when the product is stable under basic conditions. An alternative reduction to the alkane is the Clemmensen reduction, where an aldehyde or ketone is heated with amalgamated zinc in hydrochloric acid

Answer 11

carbonyl

Question 12

Aldehydes and ketones can act as nucleophiles when they undergo rearrangement to a slightly different form. ___ alpha to carbonyl groups (one carbon away) are relatively acid (pK sub a =20), due to resonance stabilization of the conjugate base. A hydrogen atom that detaches itself from the alpha carbon has a finite probability of reattaching itself to the oxygen instead of the carbon. Therefore, aldehydes and ketones exist in solution as a mixture of two structural isomers, the familiar keto form and the enol form, representing the unsaturated alcohol (ene = the double bond, ol = the alcohol, so ene + ol = enol). The two isomers , which differ only in the placement of a proton, are called tautomers. The equilibrium between the tautomers lies far to the keto side The process of interconverting form the keto to the enol tautomer is called enolization

Answer 12

protons

Question 13

___ are necessary intermediates in many reactions in which aldehydes and ketones act as nucleophiles. The enolate carbanion can be created with a strong base such as lithium diisopopyl amide (LDA) or potassium hydride, KH, either of which remove the proton from the -OH group. The resulting nucleophilic carbanion will react with an alpha, beta-unsaturated carbonyl compound in a reaction called a Michael addition

Answer 13

enols

Question 14

A key property of aldehydes and ketones is the dipole created by the partially positive carbonyl carbon and the partially negative oxygen. The partial positive charge on the carbon creates a site for attack by a wide variety of electron-rich ___. Nucleophilic attack creates a tetrahedral intermediate in which the carbon-oxygen bond is reduced to a single bond an the oxygen carries a full negative charge. Because there is no good leaving group present in an aldehyde or a ketone, the carbonyl cannot re-form and an alcohol will be the end product after protonation

Answer 14

nucleophiles

Question 15

In the presence of water, aldehydes and ketones react to form geminal diols (1,1-diols or gem diols). In this case, water acts as the ___ attacking at the carbonyl carbon. This hydration reaction proceeds slowly; the rate may be increased by the addition of a small amount of acid or base.

Answer 15

nucleophile

Question 16

When one ___ of alcohol (the nucleophile in this reaction) is added to an aldehyde or ketone, the product is a hemiacetal or a hemiketal, respectively. When two equivalents of alcohol are added the product is an acetal or a ketal, respectively. The reaction mechanism is the same as for hydration and is catalyzed by anhydrous acid. Acetals and ketals, which are comparatively inert, are frequency used as protecting groups for carbonyl functionalities. They can easily be converted back to the carbonyl with aqueous acid.

Answer 16

equivalent

Question 17

Aldehydes and ketones react with HCN (hydrogen cyanide) to produce ____ called cyanohydrins. HCN dissociates and the strongly nucleophilic cyanide anion attacks the carbonyl carbon atom. Protonation of the oxygen produces the cyanohydrin. The cyanohydrin gains its stability from the newly formed C-C bond (in contrast, when a carbonyl reacts with HCl, a weak C-Cl bond is formed, and the resulting chlorohydrin is unstable

Answer 17

stable compounds

Question 18

___ and some of its derivatives are nucleophiles and can add to carbonyl compounds, but a different final product is created than in other nucleophilic attacks. In the net reaction, the C||O bond is replaced by a C|||N bond. in the simplest case, ammonia adds to the carbon atom and the -OH group is protonated and lost as a molecule of water. This reaction produces an imine, a compound with a nitrogen atom double-bonded to a carbon atom (A reaction in which water is lost between two molecules is called a condensation reaction.)

Answer 18

ammonia

Question 19

Some common ammonia derivatives that react with ___ are hydroxylamine (H2NOH), hydrazine (H2NNH2), and semicarbazide (H2NNHCONH2); these form oximes, hydrazones, and semicarbazones, respectively

Answer 19

aldehydes and ketones

Question 20

The ___ condensation is an important reaction that follows the same mechanism of nucleophilic addition to a carbonyl. In this case, an aldehyde acts both as nucleophile (enol form) and target ( keto form). When acetaldehyde is treated with base, an enolate ion is produced. The nucleophilic enolate ion will attack the carbonyl group of another acetaldehyde molecule. The product is 3-hydroxybutanal, which contains both an alcohol and an aldehyde group. This type of compound is called an aldol, from ALDehyde and alcohOL.

Answer 20

aldol

Question 21

When heated, 3-hydroxybutanal can undergo ___ and lose H2O to form a double bond, producing an alpha, beta-unsaturated aldehyde. This type of condensation reaction is known as the aldol condensation. The aldol condensation is most useful when only one type of aldehyde or ketone is present, since mixed condensations usually result in a mixture of products

Answer 21

elimination

Question 22

The ___ reaction is a method of forming carbon-carbon double bonds by converting aldehydes and ketones into alkenes; in other words, the C||O bond ultimately becomes a C||C bond. The first step involves the formation of the necessary reactant: a phosphonium salt rom the SN2 reaction of an alkyl halide with the nucleophile triphenylphosphine, (C6H5)3P. The phosphonium salt is then deprotonated (losing the proton alpha to the phosphorus) with a strong base, yielding a neutral compound called an ylide (pronouced “ill-ide”) or phosphorane.

Answer 22

wittig

Question 23

Notice that an ylide is a type of carbanion and has nucleophilic properties. When combined with an aldehyde or ketone, an ylide attacks the carbonyl carbon, giving an intermediate called a betaine, which forms a four-membered ring intermediate called an oxaphosphetane. This decomposes to yield an ___ and triphenylphosphine oxide

Answer 23

alkene

Question 24

The ___ reaction is driven by the strength of the phosphorus-oxygen bond that is formed. Although the overall mechanism has many complex steps, the net reaction is simply the substitution of a C||C bond for the original C||O bond of the cyclic ketone

Answer 24

decomposition