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Gabriella Fiorino

Chapter 21 Study Guide

Nomenclature (21.2)

With aldehydes:

· If on a carbon chain that’s not cyclic, end the name in “-al”

· If on a ring, end the name in “-carbaldehyde”

With ketones:

· End name in “-one”

Enals: compounds with double bond adjacent to aldehyde

Enones: compounds with double bond adjacent to ketone (i.e. alpha, beta unsaturated carbonyl)

Boiling point, melting point, and solubility (21.3)

Ketones and aldehydes:

· Same melting point

· Ketone has slightly higher bp

· Soluble in organic solvents

· >5C = insoluble in H2O

· <5C = soluble in H2O

Spectroscopy (21.4)

IR for aldehydes and ketones

· For cyclic ketones, the C=O absorbance increases as ring size decreases, which increases ring strain

· Ketones have strong peaks at 1715 cm-

· Aldehydes have strong peak at 1730 cm-

· Sp2 hybridized C-H bond has 1-2 peaks at 2700-2830 cm-

Conjugated C=O has lower wavenumber

· i.e. alpha, beta unsaturated carbonyl has a lower wavenumber than a regular ketone

NMR for ketones and aldehydes:

· protons on alpha C absorb 2-2.5 ppm

· carbonyl C absorbs at 190-215 ppm

· sp2 hybridized C-H of aldehyde, the H absorbs far downfield (is highly deshielded) at 9-10ppm

keto-enol tautomerization (21.6)

Keto form is major form in the body, so the body converts enols to ketos (you’ll learn more about this in future classes and why it happens, but just so you know it’s not useless when we do these mechanisms lol)

Some reagents for keto-enol tautomerization (check out lecture notes for more):

· 1) BH3,THF; 2) H2O2, OH-

· Anti-markovnikov

· H2O, H2SO4, HgSO4

· Markovnikov

Another reagent in the chapter (21.6)

O3 with Zn, H2O or CH3SCH3:

· Turns alkenes 1 COOH and 1 aldehyde

Know what it looks like (21.7)

Enolate, imine, carbinolamine

Enantiomer vs. diastereomer (21.8)

Orgo 1 recall:

· Enantiomer: change configuration or all chiral centers

· Diastereomer: change configuration of any chiral center(s), but not all

Cyanohydrins (21.9)

Know what it looks like and how to form it (it’s a simple mechanism, so don’t memorize how to form it, just understand how to do it)

Recall: CN is a Nu- only reagent

Found in fruits and medications:

· Linamarin

· Amygdalin (in seeds and pits of some fruits)

· Laetrile

Wittig (21.10)

A Nu- used to form alkenes:

· Converts aldehyde or ketone C=C

· Coupling reaction

· Always gives a single constitutional isomer, so synthesis is favorable

· Is an organophosphorus

· Ylide (when it has 2 oppositely charged atoms bonded together & both atoms have octets)

· Forms 2 new C-C bonds (1 sigma and 1 pi) + phosphorous by-product Ph2P=O

· Be able to comfortably convert from double bond form of Wittig to ylide form

· Might have to know mechanism (refer to lecture notes)

· Dr. Frazer might want for you to know how to prepare the ylide reagent (refer to lecture notes)

Schiff Base (21.11)

Might have to know mechanism (refer to lecture notes)

Primary amine:

· Turns aldehyde or ketone imine

Has carbinolamine and iminium ion intermediates

Rhodopsin:

· Involved in vision

· Highly conjugated imine

Enamine (21.12)

Enamine: alkene adjacent to amine (know what it looks like and compare/contrast with what imine looks like)

Might have to know mechanism (refer to lecture notes)

Secondary amine:

· Turns aldehyde or ketone enamine

Mechanism: Nu- addition of secondary amine followed by elimination of H2O to get iminium ion intermediate.

Formation of imines and enamines are reversible reactions:

· Hydrolysis of imines and enamines form aldehydes or ketones (may have to know this mechanism as well, refer to lecture notes)

Gem diols (21.13)

Also called “hydrates”

Certain cabonyls gem diol using H2O

(see picture below for which carbonyls it can react with)

Formation depends on stability of starting material:

· The less stable the starting material (the more e- withdrawing groups near C=O), the more likely to form gem diol.

· The more stable the starting material (the more e- donating groups near the C=O), the less likely to form the gem diol (more likely to keep starting material)

Might have to know mechanism (refer to lecture notes)

Protecting groups (21.15)

Acetals: protecting groups for aldehydes and ketones

· Same system as when we used TBDMA and Bu4N+F- for alcohols

· Steps when using protecting groups:

· Put on protecting group (PG)

· Carry out reaction

· Take off PG

Protecting group reagent:

(this reagent is used to form acetals. The reagent itself is not an acetal)

Acetal, hemiacetal, cyclic hemiacetal (21.16)

Compare/contrast what acetals, hemiacetals, & cyclic hemiacetals look like

Cyclic hemiacetals

· Also called lactols

· 5 or 6 membered cyclic hemiacetals are very stable

· 5 membered = furanose (thing F for Five)

· 6 membered = pyranose

Know how to form acetals, hemiacetals, and cyclic hemiacetals

· Hemiacetals are an intermediate in acetal formation

Can also convert from cyclic hemiacetal to cyclic acetal

· When doing this mechanism, only the hemiacetal OH reacts (no other OH react on the ring. The hemiacetal’s OH is resonance stabilized so can react, but other OHs on the ring are not so are BAD leaving groups. No touch).

Carbohydrates (21.17)

Carbohydrates:

· Sugars and starches

· Are polyhydroxy aldehydes and ketones, or compounds that can be hydrolyzed to them

· 1 of 4 main molecules responsible for structure and function of all living cells

· Many contains cyclic acetals or hemiacetals

· Glucose

· Lactose

· Formed by cyclization of hydroxy aldehydes

· 6-membered ring preferred

· New stereogenic center formed

· The new OH can be either equatorial or axial in chair conformation

· For glucose, results in 2 cyclic forms:

· Beta-D-glucose (equatorial OH) (major product)

· Alpha-D-glucose (axial OH) (minor product)

Have complements, comments, or concerns about the tutoring session? Click the link below to rate your tutor, Gabriella F.! :D It would make her very happy :D https://ucf.qualtrics.com/jfe/form/SV_0jGMQ3pjtwHlzyR

References:

Klien, D.R. (2015). Organic Chemistry: 2ndEd. Wiley: NJ. Print.

Smith, J.G.Organic Chemistry 5th edition. McGraw Hill.

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