Organic Chemistry ACS

find the longest continuous carbon atom chain contianing the carboxylic acid group

-oate

identify the alkyl group that is in the ‘alcohol’ portion of the molecule and name it; then identify the acid part of the molecule. The ester is named with the alkyl part first, and the acid part is named as a carboxylate.

exact 2 subsituents

More covalent bonds is more stable

Separation of charges cost energy and results in a less stable resonance contributor

True

True

Reagent is peracid (COOOH) ; alkene to an epoxide; maintain stereochemistry

BH3, Et2O

When the H adds to the carbon with the fewest attached hydrogens

H and B add to the same face of the alkene.

Halide component of HX bonds adds to the more highly substitued carbon, whereas the hydrogen prefers the carbon which already contains more hydrogens.

reagent is h2so4, heat or so3 (fuming h2so4)

Ortho or para directing

meta directing

O, NR2, NH3, OH, OR, NHCOR, OCOR, R, BENZENE, C=CR2,

-X, COH, COR, COOR, COOH, COCL, CF3, CN, HSO3-, NH3+ NR3+, NO2+

increase

decrease

Those that occur through the pi system and can be represented by resonance structures

Those that occur through the sigma system due to electronegativeity type effects.

Atoms adjacent to the pi system activate the aromatic ring by increasing the electron density on the ring through a resonance donating effect. (ortho-para directing)

EWGs with pi bonds to electronegative atoms adjacent to the pi system deactivate the aromatic ring by decreasing the electron density on the ring through a resonance withdrawing effect. (meta directing)

inductive electron withdrawing and resonance donating (electronegativity and lone pair donation)

reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a beta hydroxyaldehyde or b-hydroxyketone, followed by dehydration to give a conjugated enone.

Freely rotate the bonds (change the position of the OH and CH2OH in the fischer projection, then the oyxgen-H bond will nucleophilically attack the carbon, kick the double bond of the oxygen to the oxygen to form an oxygen anion and then get protonated by a hydrogen from the alcohol gorup used to nucleophilically attack the carbon. (mechanism is in notebook)

Correy Fuches

ketone; alkene

A reducing agent; carboxylic acid and ester can be reduced by this in addtiiton to aldehydes or ketones

antiadditon or syn addition of H and Br. Antimarkovnikov.

NaOEt –> PhCh2Br –> H3O+, heat (Remove CO2)

is the alkaline hydrolysis of the fatty acid esters. Example: The chemical reaction between any fat and sodium hydroxide is a saponification reaction. triglyceride + sodium hydroxide (or potassium hydroxide) → glycerol + 3 soap molecules
Carbonyl attack

an organometallic chemical reaction in which alkyl, vinyl, or aryl-magnesium halides (Grignard reagents) add to a carbonyl group in an aldehyde or ketone. This reaction is an important tool for the formation of carbon-carbon bonds.

Treat magnesium, and then you treat the Grignard with a strong acid. This gives you the alkane. You can also use this to introduce deuterium (D) into molecules! The first step is to make the Grignard reagent

shows no splitting at all; it consists of a set of single
peaks, one for each carbon or each set of equivalent carbons in a molecule. (EXAMPLE in the exam is that benzene is basically meso, so the signals must be individual 6 signals on their own.

claisen condensation between esters containing alpha hydrogens, promoted by a base such as sodium thoxide, affords beta keto esters.
(use stronger bases to increase yield: NaH)

Aldehydes and Ketones

Carboxylic acids and esters

Because the Al-H bond is weaker and thus less stable than B-H bond.

RCH2NH2

From C=C to epoxide ; ring closure forms via a intramolecular SN2 reaction.

Cylic ether with a three atom ring; ring approximates an equilateral triangle ; making it pretty reactive, more than other ethers produced on a large scale.

mCPBA or a base

Used in oxidation of primary alcohols to aldehydes; and oxidation of secondary alcohols to ketones ; usually used to oxidize alcohols into carbonyl compounsd

Reaction which involves the reaction of an aldehyde or ketone; The phosphoran (PH3P= CR3R4 can be used to produce an alkene, but then proceed to form an unstable 4 membered ring.

Alkene CH2 is formed; PH3P=O by product.

Forms into an epoxide!!

OH OH; BREAKS apart the ether

Good lewis acid catalyst

Wolff Kischner reduction; used to convert carbonyl functionalities into methylene groups; forms R,R=N-NH2 ; or just CH2!! The imine intermediate forms tho

Benzene ring double bonded N-NH2

Polyamide ; 6 long carbonyl at each end of the chain; 4 carbons in between each of them; then 6 carbons in between each amine group

Alcohol , isocyanate, and ester like amide like thing. (RCOONHR)

phenol group, formaldehyde

COOH (CH2)5 and NHCOCH25NH2

HOCH2CH2OH ; dicarboxylic acid with benzene in between total chain looks like O-CH2-CH2-O-COC6H4-CO

equatorial

2C+2-H-X-N/2

2^n

R,R, S,S
R,S, S,R

R,S, R, R
R,S S,S

True`

Form usually with least sterically hindered ‘H’ — makes least substituted Alkene

Anticoplanar ~~

Sulfuric acid and phosphoric acid

Temperature dependent on the structure of the alcohol.

Primary alcohols

two halogens bound to the same carbon atom

Alkynes (pka 25, alakene pka = 44 , alkanes pka =50

NaNH2, in liquid NH3

Alkyne with sodium ion attracted to the carbanion

To nucelophilically attack a primary alkyl halide and form an alkyne with an acetyl group attached to it.
Or
To eliminate a beta hydrogen from the primary alkyl halide to form a triple bond with a RC=-CH and an alkene

Hydrogen adds to alkenes in the presence of metal catalysts

Insoluble platinum, palladium or Ni catalysts

Rhodium or Ruthenium based; wilkinson’s catalyst Rh(C6H5)3P)3cL

Because an unsaturated compound becomes saturated with hydrogen compound

Ni, Pd, Pt, Rh(C6H5)3PI3Cl

P-2 catalyst nickel boride (Ni(COOCh3)2) results in the syn addition of one equivalent of hydrogen to a triple bond; thus yielding a cis double bond.

reagent: H2/Ni2B(P-2)

Lindlar’s catalyst

H2, Pd/CaCO3 ; quinoline

Dissolving metal reaction which uses lithium or sodium metal in low temperature (NH3 or NH2 solvent) produces trans alkenes

reagent: Li, C2H5NH2, -78 deg C, NH4Cl

trans-alkene

Trans

No

Yes

In the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent attached itself to a carbon atom of a double bond so as to yield the more stable carbocaiton as an intermediate

When a reaction can potentially yield two or more constitutional isomers actually produces only one or a predominance of one isomer.

Get a chiral molecule, but racemic mixture (R/S) is produced becuase the carbocation is achiral (can attac with the nucleophile from both top and bottom)

form an alkyl hydrogen sulfate which is soluble in water; isopropyl hydrogen sulfate

Will form 2-propanol

Form Markovnikov addition of water (markovnikov is adding the H to the Carbon with more H’s and add nucleophile to the carbon with less H’s

Addition of a small amount of acid and large amount of water

Concentrated acid with little water present

markovnikov; gives high yields of alcohols and avoids rearrangements;

antimarkovnikov syn hydration; adds water to alkenes;

BH3, THF, H2O2, OH-

Hg(OAc)2, THF-H2O, NaBH4, OH-

Because the bulky boron group can approach the least sterically hindered carbon more easily.
– leads to anti-markovnikov product

Acid-catalyzed hydrolysis: Markovnikov addition
Oxymercuration: Markovnikov addition
Hydroboration-oxidation: antimarkovnikov and syn addition

Get vicinal dihalides; antiaddition; reaction is used as a test for alkenes because the red color of the bromine reagent disappears when an alkene or alkyne is present; allkanes don’t react with bromine in the dark

Alkene
+Br2 –> room temperature, dark, CCl4 –> vicDibromide (colorless)

SN2 attack on the bromonium ion intermediate; forms trans-1,2-dibromocyclopentane enantiomers

Water acts as nucleophile to open the halonium ion; product is halohydrin C4H4X2

X2, H2O, alkene

Divalent but have neutral carbons with a lone pair of electrons; very reactive

Heat or light intiated decomposition of diazomethane; react with alkene to form cyclopropane.

carbene-like species that reacts with alkenes

syn addition; using reagents OSO4 or KMno4, the alkeen will form 1,2 -diols

Hot KMno4, OH-, H2O, heat, H3o+
These steps can be used as a chemical test for alkenes in which the purple color of the KMnO4 dissapears and forms brown MnO2, residue if alkene or alkyne is present.

Cleavage of alkenes with ozone and workup with zinc in acetic acid leads to less highly oxidized carbons than products from cleavage with hot KMNO4.; unsubsituted carbons are oxidized to formaldehyde, mono=aldehydes, disub= ketones

reagents: o3, ch2cl2, -78 deg C, Zn/HOAc

trans product added to an alkene; if you want to go all the way –> for tetrabromoalkane or tetrachloroalkane. (2 halides per each carbon; but u have to increase the equivalents used.

markovnikov and gem-halides; addition of hydrogen halides occurs once or twice depeding on molar equivalents

reagent (HBr)

antimarkovnikov

use O3 and HOac or hot kmno4m Oh-, H3+
both forms 2 carboxylic acids

Upfield

Downfield

single unique set of protons

Signal of a given proton will be split by the effect of magnetic fields associated with protons on adjacent carbons (adjacent hydrogens +1 = peak)

– hydrogen atoms in the molecule feel different magnetic fields depending upon their location and the neighbor they directly attach to.

– nucleus feels weaker magnetic field; shielding is a barrier made of inner-shell electrons and it decreases the nucleus’ pull on the outer electrons

– nucleus feels stronger magnetic field; deshielding is the opposite of shielding. When we say that an atom is deshielded, we mean that a nucleus whose chemical shift has been increased due to removal of electron density, magnetic induction, or other effects.
– essentially other atoms (more electronegative) are trying to pull the electrons away from the Hydrogens making the hydrogens more deshielded.

H-P; p=2.2, C=2.5

F= 4.0
O=3.5
N= 3.0; Cl=3.0
Br=2.8
I= 2.5; S=2.5; C= 2.5
P=2.2
H=2.1

If replacment of each of the two hydrogens by some group leads to enantiomers, those hydrogens are enantiotopic **enantiotopic hydrogens have the same chemical shift and appear in the same signal.
– if replacement of each of the two hydrogens leads to diastereomers, the hydrogens are diastereotopic; diff shifts diff signals.

Process of removing the coupling of H to an attached carbon is called BB (broadband) proton decoupling- most CNMR consisit of a single peak for each unique carbon

– depend on the electron density around the carbon nucleus
– decreased electron density causes the signal to move downfield (Deshielding)
– increased electron density causes the signal to move upfield (shielding)

carbon alkanes are off to the right; Cl,Br, ~20-60 ppm, OH is similar (40-60); alkyne is 80 ppm; benzene is (120-140 ppm), alkene is around (120-140) ; amide is 160 , carboxylic acid is around 170-180, ester is around 160-180) and ketone and aldehydes are 190- 220

Removes all the info about the hbumber of hydrogens attached to each carbon; removes someof the coupling of carbons to hydrogens so that the coupled peaks will not overlap

Produces a spectrum of masses based on the structure of a molecule; a mass spectrum is a plot of the distribution of ion masses corresponding to the formula weight of a molecule and/or fragments derived from it;
– x axis represents the masses of ions produced
– y axis represents the relative abundance of each ion produced
– use fragmentation to impart the ions
-fragments are sorted accroding to their masses to charge ratio (m/z)
– most of the fragements detected have charge +1; the net effect is sorting of the ions by mass (m/z)
– alkyl substitued benzenes often lose a hydrogen or alkyl group to yield the relatively stable tropylium ion
– other substitued benzenes usually lose their substituents to yield a phenyl cation

loss of water

Homolytic bond cleavage –> radicals are highly reactive and short lived
– relatively weak bonds such as O-O, X-X can occur with the addition of energy in the form of heat or light
ex. dialkyl peroxide –> alkoxyl radicals

halogen radical can react to pair with its unshared electron
(alkane –> alkyl radical R)

Atoms have higher energy (less stable) than the molecules they can form; the formation of covalent bonds is exothermic
– breaking covalent bonds requires energy (endothermic)
– homolytic bond dissociation is DH = positive)

Tertiary > secondary > primary > methyl

alkanes undergo substitution reactions iwth halogens such as fluorine, bromine, and chlorine in the presence of heat or light ; forms hydrogen halide

Just use halogens (usually most if not all will react) – but the some of the number of moles of each halogenated methane produced equals the number of moles of methane that reacted).

– methane +x2 –> heat or light –> tetrahalomethane

Use a large excess of methane – to make a monohalogenated produced and an excess of unreacted methane (large excess of alkane 🙂 )

methane + x2 –> heat or light –> halomethane

-Chlorine is relatively unselective and doesn’t greately distinguish between type of hydrogen –> leads to monochlorinated product (and more substituted product) +polychlorinated products +hcl

chain initiation

fluorine > chlorine > bromine > iodine

Fluorination has a low value for Eact for the first step and is extremely exothermic therefore fluorination reactions are explosive
Chlorination and bromination ahve increasinlgly higher values of Energy of activation and lower delta H values which makes these halogenation reactions less vigorous
Iodonination has a prohibitively high value for Eact of the first step and the reaction does not occur

Bromine is much less reactive but more selective than chlorine ** tertiary hydrogens are the best

Forms diastereomers (non superimposable ; chlorine attacks from the carbocations both sides (intermediate radical is chiral; and reactions on the two faces of the radical are not equally likely.

– antimarkovnikov addition; in the presence of ROOR (peroxide) give an anti-martkovnikov addition (br adds to the least substituted)

Markovnikov addition (bromo will add to the tertiary hydrogen; most substituted in the absensce of peroxides)

Radical reaction

groups attached to the oxygen are listed in alphabetical order;
CH2OCH2CH3 is ethyl methyl ether
-ethers have an alkoxyl substituent on the main chain
– 2-methyoxypentane
– cyclic ethers can be named using the prefix ‘oxa’
Three membered ring ethers can be called exiranes
Four membered ring ethers can be called oxetanes

also known as tetrahydrofuran

Alcohol; because they have capability of hydrogen bonding
-ether boiling points are roughly comparable to hydrocarbons of the same molecular weight

Acid-catalyzed hydration of alkenes — reversible reaction with markovnikov regioselectivity –> alkene + HA –> C-C-H +A- forms an alcochol and a C-H
–>oxymercuration demercuration (
–> hydroboration-oxidation (antimarkovnikov, syn addition)

conjugate base is not well solvated so it is not as stable

H2O > ROH> RC=-CH> H2>NH3 > RH

1) Phosphorous tribromide (PBr3)
2) Thionyl chloride (SOCl2)
3) hydrogen halides (HBr)

SN1 mechanism for tertiary, secondary, and allylic and benzylic alcohols; these reactions are prone to carbocation rearrangments ; first oh group on the alkyl group is converted into a good leaving group –> then after it leaves a carbocation is formed –> halide (a good nucleophile) reacts with the carbocation
– primary and secondary chlorides can only be made with the assistance of a lewis acid such as zinc chloride

HI> HBr > HCl > HF

primary and secondary

base reacts with the S ; oxygen anion pushes electrons back down, cl leaves, then base takes the H to form the alkyl methanesulfonate

Sulfonate ion (weak base) is a good LG

1 alcohols can dehydrate into ethers ; use h2so4; temperatures may differ – high temp will cause elimination; 140 deg C is ok; 180 will cause elimination

base attacks acid, gets protonated H2O + good leavingr group, HSO4- is still present, then another molecule (alcohhol) has to act as the nucleophile and will cause the leaving group to leave. The alcohol now has the OH still but since there are two CH2CH3 and CH2CH3 at each end of the oxygen, the H must go to reduce the + charge on oxygen, then the h2o comes in to remove the H+ and form the ether.

How to synthesize unsymmetrical ethers ; sodium alkoxide attacks the alkyl halide, alkyl sulfonate, or dialkyl sulfate (shown in picture) – then the ether is formed ; along with Na+ L- (lg)

– typical substrates (unhindered with a good LG) are the following — 1 or 2nd alkyl halides, alkyl sulfonates, dialkyl sulfates
– L , – Br, -I, -OSO2R” or – OSO2R”

Alcohol is the nucleophile used in the analogous reaction to form alcohols from alkenes

– First formed using H2SO4 and CH2=C(Ch3)2 –> Protects the ether ; NaC=-CH (refer to ch 11 slide 17) ; forms a tert-butyl ether so that alkynes dont want to attack, or alkylation doesnt want to attck because of hindrance. can be removed using dilute acid (H3O+/H2O)

TBDMS ether is common (tert-butyl dimethysiyl.
The protecting group is introduced by reaction of the alochol with chlorosilane in teh presence of an aromatic amine base such as imidazole or pyridine
– can be removed by treatment with fluoride ion (tetrabutyl ammonium fluoride)

generally unreactive,
– except for cleavage by very strong acids to form the corresponding alkyl halides (where they og came from)
-dialkyl ethers (CH3CH2-O-CH2CH3) undergo SN2 reaction to form 2 equivalents of the alkyl bromide

(ch3ch2-br +h2o)

ref to slide 19 – ch 11

3 membered ring cyclic ethers ; called oxiranes (tetrahydrofuran)

Formed by reaction of alkenes with peroxy acids (commonly used peroxy acid is MMPP – magnesium monoperoxyphthalate) ‘epoxidation’ and involves syn addition of oxygen ;

– Alkene + RCOOOH
forms
– epoxide + Carboxylic acid

– epoxidation is stereospecific
– epoxidation of cis-2-butene- gives the meso cis oxirane, epoxidation of trans-2-butene gives the racemic trans oxirane

CIS -> MESO
TRANS -> RACEMIC

Considerably more reactive than ethers; this is because of their three-membered ring, which is highly strained ant therefore very reactive.

– an acid catalyzed opening of an epoxide occurs by intial protonatation of the epoxide oxygen, making the epoxide even more reactive (protonated epoxide), a weak electrophile will come in and cause the bond to break between one of the ether carbosn and the oxygen; this will form a protonated diol ; but the ultimate form will be O-C-O-C-O-H 1,2 diol + h3o+

– unsymmetrical epoxides, the nucleophile attacks primarily at the most substituted carbon of the epoxide (whichever has more carbons attached to it)

Nucleophile attacks at the least sterically hindere carbon of the epoxide (less CH3 AREA)

Open the epoxide with water under acid catalyzed conditions gives the trans diol;

– to form the epoxide from an alkene and a peroxide (MMPP) –> epoxide ring; then will be treated with an acid (COOH); causes the bond of the O to break, then OH;OH on each one (TRANS TO ONE ANOTHER)

– a cis butene forms trans enantiomeric
– trans butene forms a meso butanediol. (this is when we form the diol)
previous when you form the epoxide, the cis forms the meso epoxide and the trans forms the enantiomeric epoxide

sp2 hybridized and is trigonal planar (120)

Primary alcohols –> oxidized to aldehyde
Aldehyde –> reduced to primary alcohol

Turns into an aldehyde

Turns into alcohol

RCH2OH

Formaldehyde (or aldehyde)

Carboxylic acid (highest oxidation state)

1) COOH – carboxylic acid
2) RCOOR – ester
3) RCOH – alcohol
4) RCOR – ketone

primary alcohol

liAH or high pressure hydrogenation can accomplish this transformation

Aldehydes and ketones are reduced relatively easily; the mild reducing agent sodium borohydride (NaBH4) is typically used
LAH and hydrogenation with a metal catalyst can also be used

LiALH4 is very reactive with water and must use an anhydrous solvent such as ether ;
Nabh4 on the other hand ican be used in solvents such as water or an alcohol

PPC – pyridinium chlorochromate (made form chromium trioxide under acidic conditions) used in organic solvents such as CH2CL2

KMnO4 ; in aq solution

H2CrO4 (chromic acid) and Jones reagent (CrO3 in acetone)

Chromium oxide has a clear orange color which cahnges to a greenish opque if a oxidizable alochol is presnet

3200-3600 cm -1

3.3 – 4.0

50-90

Carbon-metal bonds varying widlely in character from mostly covalent to mostly ionic depending on the metal

– greater the ionic character, the more reactive the compound ; organopostassium compounds react explosively with water and burst into flame when exposed to air.

R-X +2Li –> et2o –> RLi + LiX

Reacting organic halides with magnesium turnings; ether solvent is used because it forms a complex with the grignard reagent which stabilizes it

– RX +Mg –> Et2o –> RMgX
– ArX +Mg –> Et2O –> ArMgX

ex. Ch3I +Mg –> Et2o –> Ch3MgI
C6H5Br + Mg –> Et2o –> C6h5mgBr

– organolithium and grignard reagents behave as if they were carbanions and they are threrfore very strong bases — react readily with hydrogen atoms attached to oxygen, nitrogen or sulfur in addition to other acidic hydrogens

–> form alkane (weaker acid) and alkoxide ion (weaker base)

– useful nucleophiles for C-C bond synthesis

Reaction results in ring opening and formation of an alcohol product; reaction occurs at the least-substituted ring carbon of the oxirane

Nucleophilic attack of carbonyl carbons is the most important reaction of grignard regeants;

– grignard’s with aldehydes and ketones yields a new carbon-carbon bond and an alcohol

– form alcohol, h2o, mgx2

primary alcohol (H3o+ used to supply the H)

secondary alcohol (h3o+ used to supply the H)

tertiary alcohol (NH4Cl is used to supply the H

– ketone formed by the first molar equivalent of Grignard’s reagent; reacts a second equivalent to produce the alcohol
– final product contains two identical groups at the alcohol carbon that are both derived from grignard’s

– 2 equivalents of grignards – along with an alcohol group and R’ (forms a 3 alcohol)

– The acidic hydrogens will react first and will quench the Grignard reagent;
– two equivalents of grignard reagent could be used so that that first

Attack aldehyde or ketone, form lithium alkoxide –> hydrolyse –> alcohol

They react with carbonyl compounds such as aldehydes and ketones to form new carbon-carbon bonds

Corey-Posner, Whitesides-House synthesis ;
Alternative formation of carbon-carbon bonds which, couples two alkyl halides

-RX +R’X –> R-R’

Any alkyl halide –> RLi –> Cui –> R2CULi –> RX –> R-R’ +RCu +LiX

have a p orbital on a carbon adjacent to a double bond; p orbital can come from another double or triple bond ; the p orbital may be the empty p orbital of a carbocation or a p orbital with a single electron in it (radical)

-why are they good? — special stability to the molecule
– conjugated molecules can be detected using UV spectroscopy

Depends on reaction conditions; at low temperature the halogen adds across the double bond; at high temperature or at very low concentration of halogen, an allylic substitution occurs
(addition)
CH2=CH-CH3 +X2 — low temp/CCl4 –> Ch2 -X – CH – X – CH3
(substitution)
CH2 = CH-CH3 +x2 — HIGH TEMPERTUARE OR low concentration of X2 –> CH2 = CH – CH2X +HX

High temperature in gas phase; reaction is a free radical chain reaction; in the initiation step a low concentration of chlorine radical is produced; int eh first proapgation step an allyl radical is formed , in the second propagation step the allyl radical reacts with moelcular chlorine

Because they are more stable than ordinary primary, secondary, tertiary, or vinyl radicals ; of all the dissociation energies, the allyl radical is the lowest, and the vinyl radical is the most.

allylic > 3 > 2 > 1 > vinyl

Use NBS (N-bromosuccinimide) in the presence of light or peroxides (propene –> 3-bromopropene)

N-Bromosuccinimide converts into Succinimide.

– A bromine radical reacts with propene to produce an allylic radical and HBr
– HBr reacts with NBS to produce a bromine molecule (radical
– a molecule of bromine reacts with a propene radical to regenerate a bromine radical

MO description; when an allylic hydrogen is abstracted to form an allyl radical, the developping p orbital on the sp2 carbon overlaps with the p orbitals of the alkene ; new p orbital is cojugated with the double bond p orbitals; the radical electron and the pi electrons of the alkene are delocaized over teh entire ceonjguated system; delocalziation –> increased stability.
– three p orbitals of the allylic system combine to form three molecular orbitals (bonding molecular orbitals contains two spin-paired electrons and this orbital increases bonding between the carbons
– the non bonding orbital contains a lone electron which is located at carbons 1 and 3 only.

Contain 2 double bonds

Conjugated dienes affect each other when they react, isolated doubel bounds react separtaely and do not affect each other; cumulated are just all in one row ; no separation between p orbital and s orbital.

1.34, 1.47, 1.34 A; the central bond is shorter than that in ethene for two reasons – the signma bond between C2 and C3 is made from sp2-sp2 overlap

s-cis and s-trans
s indicates that the conforamtions orginate from rotation around a single bond; s-trans is more stable because it is less sterically hindered.

The wavelength of radiation absorbed and the intensity of the absorption depend on the structure of the molecule
– the uv vis spectrum is typically measured from 200-800 nm

In UV-vis spectroscopy the electrons are excited from lower energy leve3ls to higher nes;
– the electron is generally excited from the highest occupied molecular orbital (HOMO) to the lowest unoccupied moelculcular orbital (LUMO)
– alkene and nonconjugated dienes ahve absorptions below 200 nm because the energy difference between the HOMO and LUMO is large
– in conjugated dienes, these energy levels are much closer together and the wavelengths of absorption are longer than 200 nm.

the smaller the energy difference between the HOMO and LUMO;

carbonyl compounds; unsahred electron on oxygen is promoted into the pi 3

At room tmeperature (78%) additon 1,2; at n

planar monocyclic rings with continuous system of p orbitals and 4n+2pi electrons are aromatic (n=0,1,2,3)

Deriving the relative energies of orbitals of a system with a cyclic continuous array of p – orbitals; polygon corresponding to the ring is inscribed in a scircle with one point of the polygon pointing directyly down; horizonta line is draw where vertices of the polygn otoucht ehc circle — each line corresponds to the energy level of the MOs at those attooms; a dashed horizontal line halfway up the circle indicates the separation of bonding and antibonding orbitals.

adopts a nonplanar conformaiton with localized pi bonds to avoid instability

Monocyclic compounds with alternating double and single bonds;

named using a number in brackets that indicates the ring size
ex. benzene is [6] Annuelene and [8] annuelene is cyclooctatraene

– [14] annulene, [18] annuelene ; [16] annulene is NOT aromatic;
– [10] annuelen should be aromatic but none of them can be planar; angle strain, steric interaction or etc.
– cyclobutadiene is [4[ annuelen and is not an aromatic – it does not follow the 4n+2 rule and is highly unstable

Provides regions of great shielding ; large annulenes tend to be highly shielded; protosn outside the ring appear at 9.3 (highly deshielded) whereas those on the inside of the ring tend to appear at -3.0 (highly shielded)

Because it becomes the aromatic cyclopentadienyl anion when a proton is removed; cyclopentadienyl anion has 6 pi electrons in a cyclic, continuous pi electron system ; thus it is aromatic
cycloheptatriene is not aromatic because its pi electrons are not declocalized around the ring

Have two or more benzene rings fused together
ex. naphthalene, etc.

three resonance structures; show that 10 pi electrons of napthalene are delocalized and that it has substantial resonance energy; EXCEPTION: pyrene has 16 pi electrons; but is known to be aromatic; ignore the central double bond.

Dont contain benzene rings, azulene has substance resonance energy and also substantial separation of charge

Bucky ball; C60 compound with interconnecting pentagons and hexagons; each carbon is sp2 hybridized and has bonds to 3 other carbons;

Have an element other than carbon as the mmeber of the ring; ex. pyridine, pyrrole, furan, thiophene
– pyridine has an sp2 hybridized nitrogen; the porbital is part of the aromatic pi system of the ring; nitrogen lone pair is in a sp2 orbital orthogonal to the p orbitals;
– lone pair on nitrogen is avaliable to react with protons so pyridine is basic.

C-H stretching occurs near 3030 cm-1; stretching motions of th ering give bands at 1450-1600 cm-1 and two bands near 1500-1600 cm-1;

moderate intensity near 205 nm, less intesnse band at 250-275 nm.

major ion in mass spectrum of alkyl benzenes is m/z 91; corresponds to C6H5Ch2+ which rearranges to a tropylium ion

– Aromatic compounds under electrophilic aromatic substitution; aryl group is removed by removal of a hydrogen atom from an arene

x2, FEX3,

HONO3, H2SO4

SO3, H2SO4

RCl2, AlCl3

acyl chloride and alcl3

– benzene reacts with an electrophile using two of its pi electrons; reacts further;
– forms a arenium ion; which is stabilized by resonance which deloca;zises the charge; step 2 proton is removed and the aromatic system is regenerated (this time with the added group / electrophile) as the new benzene.

– need lewis acid as a catalyst;
-Cl2 and Br2 are good halogenators;
-Flurination occurs so rapidly that its hard tos top at monofluorination of the ring
-iodine is so unreactive that an alternative method must be used

Mechanism:
1. bromine reacts with ferric bromide to generate an electrophilic bromine species
2. highly electrophilic bromine reacts with pi electrons of the benzene ring; forming an arenium ion
3. proton is removed from the arenium ion and aromaticity is regenerated (Catalyst is regenerated)

Hno3 and h2so4 – form a nitronium ion ; this becomes the electrophile the benzene ring attacks.

Occurs most rapidly using fuming sulfuric acid (concentrated sulfuric acid that contains so3);
– so3 + is attacked, benzene sulfonate ion accepts a proton to become benzenesulfonic acid
– sulfonation is an equilibirium reaction, thus all steps involved are equilibrium;
– desulfonation can be accomplished using dilute sulfuric acid (high water conc) or passingsteam throught the reaction and collecting the volatile desulfonated compound as it distills with steam.

An aromatic ring can be alkylated by an alkyl halide in the presence of a lewis acid — serves to generate a carbocation electrophile

Using PCl5 or SOCl2 on carboxylic acid

Powerful EWG; amino groups also make the ring less reactive to friedel crafts rxn because they come EWG upon lewis acid-base reaction withe the lewi catalyst.

– EWG groups include:
NO2, N(ch3)3, cooh, cor, cf3, so2h , nh2

Because they do not form carbocations readily

– polyacylatiion does not occur because the acyl group deactivates the aromatic ring to further substitution

Primary alkyl halides often rearranged products in Friedel Crafts alkylation — major limintation;
– reduction reduces phenyl ketones to the methylene (Ch2) group ;

more reactive than benzene

– Ch3, NH2, OH, F, Br, Cl,

-NO2, c=OOH, Hso3, Cl- , Br-, etc, NR3,+, CF3, CCL3

lithium tri-tertbutoxyaluminum hydride

can be used to reduce ester to aldehyde at low temperature

Through ozonolysis of an alkene – O3 and Zn, HoAc –> ketone aldehyde

AlCl3 and acyl chloride

H2CrO4

R2CuLi +RCOCl –> RCOR +RCu +LiCl

Addition does not occur twice because two negatie charges on teh nitrogen would result ;

Aldehydes are generally more reactive than ketones
– the tetrahedral carbon resulting from addition to an aldehyde is less sterically hindered than the tetrahedral carbon resulting from addition to a ketone
– aldehyde carbonyl groups are more electron deficient because they have only one electron donating group attached to the carbonyl carbon.

Hemiacetals are an aldehyde of ketone dissolved in an alcohol will form the hemiacetal; hydroxyl and alkoxyl group on the same carbo, –
acyclic hemiacetals are generlly not stable,
– however cyclic five and six-membered ring hemiacetals are.

when an aldehyde or ketone is in the presence of excess alcohol and an acid catalyst will form an acetal ; combo of acid catalysed and base catalysed reactions to form the acetals

H3O+ acetal plus H2o –> aldehyde, 2Roh

Forming Cyclic 5 and 6 emmebered ring is favorable bc they are used as protecting groups for aldehyedes and ketones
– can be removed with aqueousacid okay

Protecting groups are the following: HOCH2CH2OH (excess)

An ester can be reduced in the presnece of a keotne protected as an acetal; ; use LiAlH4 in Et2O as the reducer, used H2o work up and antoher H3o+ H2O WORKUP TO REMOFE THE acetal protecting group

Thioacetals can be converted to Ch2 groups by halogenation using a catalyst such as Raney Nickel
– this sequence provides a way to remove an aldehyde or ketone carbonl carbon
– 2 CH3CH2SH –> HA
or
– HSCH2CH2SH –BF3 –> cyclic thioacetal

Treat both with Raney Ni (H2) –> RCH2R H-CH2-CH2-H + NiS

They yield imines; secondary amines yield enamines

Form cyanohydrin; a catalytic amount of cyanide helps speed the reaction ; cyanide nucleophilic attack at the carbonyl carbon; oxygen anion takes the H;

Aldehydes and ketones react with phosphorous ylide to prodcue alkenes
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