final (chapters 7 & 8) Flashcards
(98 cards)
1
Q
physical properties of alkenes & alkynes (+ what makes them gas/solid/liquid at room temp)
A
- similar to alkanes
- non polar
- soluble in nonpolar solvents
- low density ( <1.0 g/mL)
gases at room temp: C2-C4
liquids or solids at room temp: > C4
as molecular mass increases, they become liquid and then they solidify
2
Q
E/Z naming system for alkene diastereomers
A
- based on atomic number of attached atom = higher the atomic number, higher the priority
- compare both sides of the double bond and choose the higher priority group
same side = Z
opposite side = E
on the Zame Zide
3
Q
how to name E/Z system when there is more than 1 double bond
A
-diene at the end of the name
- specify where the double bond starts (ex. 1E, 4Z)
otherwise, don’t need to specify number when only 1 double bond present in the molecule
4
Q
cis vs. trans alkenes stability
A
trans alkenes: more stable due to reduced steric hinderance b/c substituents on opposite sides of the double bond
- release less heat upon hydrogenation b/c already more stable to begin with
cis alkenes: less stable b/c of stern strain b/c substituents on the same side of the double bond = more potential energy of molecule
- release more heat upon hydrogenation b/c more potential energy so to fall down to stable releases more energy
5
Q
heat of hydrogenation + which have more
A
heat of hydrogenation: energy released when alkene undergoes hydrogenation (addition of hydrogen across double bond), reflects relative stability of alkenes
- more stable alkenes = less heat released b/c they already have lower potential energy
- less stable alkenes = more heat b/c transition to stable alkane lowers energy more significantly
(think of the diagram chart thing)
6
Q
when can you compare the hydrogenations of different molecules?
A
when the product is the same (same alkane)
- when product is the same, any difference in ∆Hº are due to stability of the different alkene reactants (otherwise there are other factors unrelated to the stability of the starting alkenes)
- cannot compare heat of hydrogenations if the products are different alkanes
7
Q
what determines the relative stability of an alkene?
A
the number of alkyl groups that are attached
more the alkyl groups attached to the carbons of the double bond = more stable the alkene
- in disubstituted alkenes, trans is more stable than cis ones
8
Q
trans/cis compounds in cycloalkenes
A
- cycloalkenes with 5 or fewer carbon atoms can only exist as cis b/c they cant twist enough to become trans
- so cis is not explicitly stated in their name even though they’re usually cis
- trans- cyclohexene and trans- cycloheptene exist for very short periods and have not been isolated
- trans- cyclooctene has been isolated, molecule is chiral and exists as pair of enantiomers
- doesn’t have chiral carbons but by definition chiral means non-superimposable mirror image
9
Q
α- and β-carbons + β hydrogen atom
A
α-carbon: carbon bearing the leaving group
β-carbon: carbon adjacent to alpha carbon, hydrogen that’s attached to it is called β-hydrogen
10
Q
two specific elimination reactions: dehydrohalogenation
A
alkyl halide loses H atom and halogen (X) from adjacent carbon atoms, forming alkene
requires:
- strong base (like OH-, OR-) to abstract β-hydrogen
other strong bases:
- KOH dissolved in ethanol (important in ethanol)
- conjugate base of an alcohol (i.e. sodium ethoxide, EtONa)
- also effective is t-BuOK (potassium tert-butoxide)
- this reaction is usually E2 but if weak base & tertiary substrate is used, then can become E1
11
Q
KOH dissolved in ethanol vs. KOH dissolved in H2O
A
dissolved in ethanol = elimination reaction
dissolved in H2O = substitution reaction
12
Q
7 strong acids + 6 strong bases
A
strong acids:
HCl
HCLO3
HClO4
HBr
HI
HNO3
H2SO4
strong bases: hydroxides of group 1 and group 2 elements:
- LiOH
- NaOH
- KOH
- Ca(OH)2
- Sr(OH)2
- Ba(OH)2
- also CH3O- and EtO- and obviously OH-
13
Q
why can a carbocation be attacked from both sides and what does it result in?
A
can be attacked from both sides because its sp2 hybridized (planar)
- results in racemization (both of the enantiomers are produced)
14
Q
determining strength of nucleophiles
A
nucleophiles can behave as bases b/c of their unshared pair of electrons
strongest nucleophiles are negatively charged
atoms in same period (horizontal)** = nucleophilicty strength is same order as base strength (basicity decreases as you go to the right because of more electronegativity so electrons are more tightly held and less likely to be given since to accept proton, need to give it electrons)
atoms in same column = nucleophilicity increases going down the table
15
Q
tertiary alkyl halides never undergo which reaction but will readily undergo which reaction?
A
never go SN2 because too statically hindered but will easily undergo E2 if strong base is present
16
Q
hydrolysis reactions
A
leaving group is replaced by hydroxide (OH) forming a neutral alcohol
check the degree of the substrate to determine which type of reaction
17
Q
determining good leaving group
A
leaving group ability increases with decreasing base strength or increasing strength of leaving group’s conjugate acid
- so less basic = stronger leaving group
example: bad leaving groups are strong bases like OH- and NH2-
whereas good leaving groups are weak bases like I- and Cl- (conjugates of strong acids)
18
Q
resonance affect on nucleophilicity
A
decreases nucleophilicity because delocalizes charge across atoms, making lone pairs less available for nucleophilic attack
but in some cases, resonance can enhance if it will stabilize the nucleophile after the bond formation
19
Q
can SN1/SN2/E1/E2 reactions occur at areas not sp3 hybridized?
A
no, all of them usually require sp3 hybridization b/c they need the electrons and in sn1/e1 leads to less stability of the carbocation
20
Q
zaitsev vs Hoffman product in elimination reactions
A
Zaitsev: more stable alkene (the more substituted one)
- favored by small bases and less hindered substances
hoffman product: the less stable alkene (less substituted one)
- favored by bulky bases, steric hinderance (b/c too difficult to go around all those groups to get the H so just settles for the nearby one)
21
Q
methyl substrates will always proceed via what reaction regardless of the solvent or the base
A
SN2
- only have 1 carbon so cant even form a double bond or an intermediate carbocation
22
Q
primary substrates favor what type of reactions?
A
SN2 unless bulky base is used then E2
23
Q
secondary alkyl halide - how to determine what type of reaction will proceed?
A
SN2: strong nucleophile (CN-, I-), polar aprotic solvent (DMSO, acetone), SN2 becomes minor product if strong base is present
- also favors less steric hindrance (secondary halides without bulky groups)
SN1: weak nucleophile (H2O, ROH), polar protic solvent!! (H2O, ethanol) to stabilize the carbocation intermediate
- often competes with E1
E1: weak base, polar protic solvent, high temperature
E2: strong base, anti-periplanar β-hydrogen, high temperatures
- major product is zaitsev unless bulky base then its Hoffman product
24
Q
major/minor product when small, strong base is used (NaOEt)
A
Major is E2: Zaitsev product
minor is SN2 is the nucleophile is strong
25
optical activity
**optically active**: can rotate plane polarized light
to be optically active, molecule needs to be:
- **chiral** (no internal plane of symmetry)
- **have enantiomeric excess** (racemic mixture is optically inactive because the rotations cancel each other out
if stereochemistry of a chiral compound is *preserved*, optical activity is **retained**
- SN2's retain optical activity with inversion because chirality of carbon is preserved even though inverted
- but if racemic mixture is formed, then not always guaranteed retention of optical activity
26
rate-determining step & reaction rate of E1 reactions
**rate determining step**: loss of the leaving group, formation of carbocation
base does not participate rate-determining step so **conc. of base does not affect the reaction rate**
rate is sensitive to **nature of starting alkyl halide**
- 3º react the fastest, and 1º typically do not undergo E1 reactions (b/c rate of reaction is dependent on the stability of the carbocation)
27
E1 reactions are usually also accompanied by what reaction?
SN1
28
when can OH group participate in a reaction?
when it is first protonated, because it is a terrible leaving group
- protonated = becomes water = better leaving group
29
E1 processes when substrate is an alcohol (OH) require what
requires **use of strong acid** first to protonate the OH group
*dehydration of alcohols*
also require **heat** to break the C-OH2 bond promoting water loss, leading to the formation of the carbocation
- without heat, breaking the C-OH2 bond is unfavorable
*can also happen with low heat if alcohol is tertiary or allylic (stabilizing the carbocation intermediate) or a very strong acid catalyst is used*
30
regiochemical outcome of an E2 reaction
regiochemical means Zaitsev or Hoffman
- can be controlled by carefully choosing base
**sterically hindered base (tBuO-) = favors Hoffman product**
- b/c base has to abstract the closest proton, too much energy to go in with such a fatty
**not sterically hindered = favors Zaitsev**
31
regiochemical outcome of E1 reaction
regiochemical outcome **cannot** be controlled
**Zaitsev product** is generally obtained
32
stereochemical outcome of **E1 reaction**
E1 reactions are **stereoselective** so when both cis and trans products are possible, favors **trans alkene (E)**
- much more stable due to lower steric hinderance
cis alkene (Z) is often minor product, formed when steric effects are less significant
33
the 3 steps needed to predict what type of reaction it is
1. identify the reagent (weak/strong nucleophile/base)
- *main difference between substitution & elimination is the function of the reagent*
2. analyze the substrate and determine the expected mechanism
3. consider regiochemical and stereochemical requirements
34
function of reagent and what type of reaction it will produce
substitution = reagent acts as nucleophile
elimination = reagent acts as base
**nucleophile only**: exclusively substitution reactions (not elimination)
- *halides, sulfur nucleophiles*
**base only**: elimination occurs rather than substitution
- hydride ion, t-butO
**strong base/strong nucleophile**: generally bimolecular processes (E2 and SN2)
- *hydroxide (HO-), alkoxide ions (RO-), also t-buO- bc its strong nucleophile but rarely acts as such*
**weak nucleophile/weak base**: unimolecular processes (SN1 and E1)
- *H2O and alcohols (ROH)*
35
list reagents in each category:
- nucleophile (only)
- base (only)
- strong nuc/strong base
- weak nuc/weak base
**nucleophile only**: halides excluding F, sulfur nucleophiles excluding H2SO4 (because it only functions as an acid, neither base nor nucleophile)
- Cl, Br, I, *HS-, H2S, RS-, RSH*
**base only**: hydride ion (usually shown as NaH) - *not a nucleophile even though has negative charge because too small so is not sufficiently polarizable*
- *t-BuO-*
**strong nuc/strong base**: hydroxide (OH-), alkoxide ions (RO-)
- *EtO-, MeO-,*
- also t-BuO b/c practically is also a nucleophile but rarely acts as such since is too sterically hindered which prevents it from acting as a nucelophile
**weak nuc/weak base**: water (H2O) and alcohols (ROH)
36
relationship b/w nucleophilicty and basicity
nucleophilcity **parallels** basicity when the atoms being compared are in the same row
- *ex. N is less electronegative than O = N is better base = N is also better nucleophile*
nucleophilicity **does not parallel** basicity when atoms are in the same column
- *HS- has bigger size so is more stable = better nucleophile = but HO- is better base (b/c in the same column)*
37
why is sulfur an excellent nucleophile?
because it has a large, easily distorted electron cloud (**polarizable cloud**)
- when a **large atom** like sulfur approaches an electrophile, the electron density cloud gets polarized (like a squishy ball that can move around); this increases ***force of attraction** b/w the nucleophile and the electrophile = so attack is very fast
and **nucleophlicity = measure of how fast the nucleophile attacks**
38
what type of reaction do you have when a halide is the reagent in alkyl halides?
**substitution**
because halides almost always serve as nucleophiles, so never elimination reactions
39
allylic vs. vinylic carbon atoms
**allylic**: carbon atom is directly adjacent to a double bond
**vinylic**: carbon atom that is part of a double bond (sp2 hybridized)
40
allylic, vinylic, and benzylic, aryl carbons reactivity in substitution reactions
**allylic**: halide attached to carbon atom that is next to double bond
- *undergo SN1 and SN2 much faster than simple alkyl halides* (b/c stabilization of carbocation or less steric hinderance for SN2 attack)
**vinylic**: halide attached directly to carbon that is part of the double bond
- *rarely undergo SN reactions* b/c hard to form stable carbocation + too much repulsions from electron density
**benzylic**: halide attached one away from benzene ring
- *extremely reactive to substitution reactions*
**aryl (phenyl) compounds**: directly in the benzene ring (attached to one of the carbons in the ring)
*also does not participate in nucleophilic substitution*
**aryl & vinylic are sp2 hybridized but the other 2 are sp3 hybridized**
41
OTs
tosylate
good leaving group in organic reactions; particularly nucleophilic substitution reactions
42
when do you change a dash/wedge into a stick?
when it is no longer a stereogenic center - **becomes sp2 hybridized**
attached to a double bond now
43
stereochemical outcome of SN1 reaction
nucleophile replaces leaving group with **racemization** (results in enantiomers)
44
acetate ion
good nucleophile bc of negative charge
-O-C=O -C
45
exception of halogen attached to primary carbon where the carbon next to it is attached to many groups
follows SN1 instead of SN2 b/c even though halide itself is attached to primary carbon, too much steric hinderance near it (so nucleophile has hard time approaching)
- SN1 forms a **stable carbocation through methyl shift** and reaction can proceed
46
when does a hydride shift occur? and methyl shift?
when charge is on a 2º carbon thats NEXT to a 3º carbon
otherwise: methyl shift has to occur if methyl groups are available
**carbocations always seek stability*
47
anti-periplanar conditions of E2 reactions
in E2, the leaving group and ß hydrogen need to be across from each other (one on dash, then one on wedge)
- if not, then have to rotate them (can do that in Newman projections)
48
in addition reactions, how many products can be formed (not total) based on the # of chiral center?
going from sp2 to sp3 = chiral centers can be formed
**0 chiral centers** = 1 achiral product
**1 chiral center** = 2 products (R and S enantiomers)
**2 chiral centers** = 4 products (2 pairs of enantiomers)
unless compound is formed is **meso** (has that plane of symmetry), then would just be 1 (pick either of the enantiomers, but don't draw both)
49
how many transitions states does an E2 reaction have?
only one - new bond being formed while leaving group bond is breaking
**second-order reaction overall = bimolecular**
50
pKa of a terminal alkyne
25-26
51
in alkene addition reactions, when does the stereoselectivity matter?
**when 2 chiral centers are formed** because then you can get 4 different products
- unless reaction is specifically is syn/anti = then only 2 products formed
52
in alkene reactions, what does regioselectivity have to do with and what does stereoselectivity have to do with?
**regioselectivity**: markovnikov/anti markovnikov
- markovnikov: H goes to less substituted carbon (the one with more H's)
- anti-markovnikov: opposite
**stereoselectivity**: anti addition or syn addition
53
are terminal alkenes cis/trans?
neither
**cis-trans isomerism** only exists when each carbon of the double bond has 2 different substituents
54
cyclohexanes for E2 anti-periplanar arrangement
both leaving group and beta hydrogen need to be in the **axial position**
- naturally one up and one down when they're axial
(because they need to be aligned but in opposite planes)
if not both axial, then need to do **ring flip**
otherwise, if 1 is axial and the other is equatorial - use the one that is axial, the one thats equatorial won't eliminate
55
what do all alkenes act as in the first step of every alkene addition reaction?
nucleophile
56
bond between BH3 and alkene
**partial bond with 4 membered ring**
- happens because borane is an electron-deficient molecule b/c it lacks full octet and *alkenes have a pi bond which makes them electron rich*
57
why does Hg form a membered ring in addition reactions?
because it has so many electrons
- big electronegative metal
58
what does every attack on an sp3 hybridized carbon lead to?
inversion of configuration/ anti addition
59
which side does equilibrium in a reaction favor?
goes towards **weaker acid/base** (the one with the higher pKa
- to solve questions like these, compare the pKa's of the acid and the conjugate acid
60
wherever there is a formation of a carbocation (SN1/E1), there can be __________?
rearrangements to form a more stable carbonation
- methyl shifts/ hydride shifts/ ring expansions
61
which type of carbocation forms the fastest and why?
**tertiary carbocations** because they have a transition state that is lowest in free energy
62
what is always regenerated at the end of an acid-catalyzed dehydration of alcohol reaction?
the acid catalyst
63
which type of alcohols react most fastest when treated with sulfuric acid?
**3º alcohols** b/c the most stable carbocation intermediate formed
- also depends on concentration of acid and temperature!!
- need **concentrated acid and temp of 180º C** for primary alcohols
- **secondary alcohols**: 85% conc. + 165-170ºC
- **tertiary alcohols**: 20% conc. + 85ºC
64
when is the stereospecificity (anti-periplanar arrangement) of an E2 reaction not relevant?
when there is more than 1 beta-hydrogen atom available
**stereospecificity is only relevant when there is only 1 beta H atom available**
65
syn coplanar and anti coplanar states in Newman projection
syn coplanar = eclipsed
anti coplanar = staggered
for E2 reactions (needs to be anti and staggered in Newman projections)
66
what reaction do primary alcohols undergo dehydration by?
**E2** but product looks like it has been formed by E1
- OH group is still protonated first and then the E2 pathway happens (major product is Zaitsev)
67
protons that are available for donation (bronsted Lowry acid question)
protons available to be donated if they are **attached to electronegative atoms** (like nitrogen, fluorine, or oxygen = protic solvent too)
- alkynes are also **slightly acidic** and can donate the H as well
68
germinal dihalide vs. vicinal dihalide
**geminal dihalide**: 2 leaving groups are attached to the same carbon
**vicinal dihalide**: 2 leaving groups are attached to adjacent carbon atoms (one carbon has one and the other carbon next to it has the other leaving group)
69
How do you synthesize **terminal** alkynes from an alkyl dihalide? (Also called double dehydrogenation)
by using a super strong base like NaNH2 (use 3 equivalents of it) because the elimination (E2 mechanism only) needs to be done twice in a row
*NaNH2 is sodium amide*
- the third time, **NH2 deprotonates the alkyne** (turns it into acetylide ion which is the reason the product is so favored bc it pulls it all the way through)
- finally, in the second step, **use H2O to reprotonate** the acetylide ion (NH4Cl is used in the slides instead of water)
- in order to do this, **leaving group needs to be at the end** or at the 2nd last end of chain or vicinal (one on each carbon)
70
How do you synthesize **internal** alkynes from alkyl halides?
Use only NaNH2, this time only need 2 moles
**vicinal dihalide** required
71
What 2 reagents can be used to stop the reduction of alkynes at the alkene step?
**Lindlar’ catalyst** (Pd/CaCO3 or BaSO4/quinoline)
Or can also use **Ni2B (P-2)**
With H2 at the top of the arrow, and these catalysts at the bottom
**causes syn addition so if molecule is internal alkene it HAS to be cis**
72
rule for numbering cycloalkenes
**double bond takes priority**
- chloro group or methyl group are then numbered based on **lowest point of difference** (whatever is closer to the double bond)
*same rule applies with cycloalkynes*
- same rules apply in straight-chain alkenes and alkynes where double/triple bond takes numbering priority unless theres a functional group
73
diethyl ether as a solvent
slightly polar solvent
- can be good for dissolving both polar and nonpolar compounds (b/c the presence of O but also alkyl groups)
- so, this might make it more compatible with dissolving compounds that are polar and nonpolar both (have an ionic head but a long hydrophobic tail)
*like ammonium oleate* (huge carbon chain attached to an ammonia group)
74
the syn-addition reactions + saying to remember
- hydroboration
- catalytic hydrogenation
- epoxidation
- syn-dihydroxylation
*your **syn** is that you will **hydroborate** the earth but then **epoxy** will fight you until you **catalyze** him**
75
anti addition reactions + way to remember them
***halogens hate harmony** - the reactions with the halogens (halogenation and halohydrin formation + all the deoxymerc and mere reactions*
- halogenation
- halohydrin formation
- alkoxymerc.-demerc.
- oxymerc-demerc.
- anti-dihydroxylation
76
what does starting with a pure stereoisomer result in?
stereocenter of the product will have the same configuration as the one in the reactant
**no racemization occurs**
77
+∆G and -∆G values mean what?
+ = backward reaction is favored
(-) = forward reaction is favored
**-∆G occurs when -∆H and +∆S**
78
effect of aromatic group on acidity
aromatic group stabilizes the neg. charge making the compound more acidic
ex. phenol is more acidic than cyclohexanol b/c it has double bonded ring
79
weaker the conj base =
considered more stable conj. base (less likely to accept proton making it weaker base) making it **stronger acid**
80
How to name bicyclic compounds
- start from the bridgehead that gives the substituent (if any) the lowest number and **go through the biggest ring first**
[]= number of carbons on both sides and between the bridgehead, bigger number first
*ex. 1-isopropyl bicyclo[2,2,2] octane*
81
difference in products of alkyne ozonolysis when terminal alkyne vs when internal alkyne
**internal alkyne**: products are 2 carboxylic acids (length of each is the size of the chain attached to the triple bond)
**terminal alkyne**: products are 1 carboxylic acid and *CO2*
- this is because the terminal end forms a 1 carbon carboxylic acid which is really just formic acid (not stable at all so oxidizes further into CO2)
82
What’s different in the reaction product if you use Na/NH3 (liquid) vs when you use NaNH2/NH3 liquid?
**Na/NH3 (liquid)**: gives the trans alkene from an alkyne (dissolving metal reduction)
**NaNH2/NH3 (liquid)**: gives an acetylide ion (terminal alkyne with a lone pair and negative charge)
83
More substituted end in terminal vs internal alkynes
**terminal alkynes**: more substituted end is the one attached to the alkyl group
**internal alkynes**: no more substituted side regardless of how long the carbon chain attached is
- so markovnikov and anti-markovnikov don’t mean anything and neither does E or Z isomerism (though cis is more stable)
84
How many equivalents of reagents are used in hydrohalogenation of alkynes?
**1 equivalent**: gives you the alkene
**2 equivalents**: gives you all the way to the alkane
85
In hydrohalogenation of alkynes (adding H and a halide), how are the groups added and what is the product of the second equivalent?
Groups (H and Halide) are added in **anti-fashion** so across the 2 hydrogens, they’re on opposite sides
And the second equivalent gives a **geminal dihalide** (both halide groups are on the same carbon)
86
reagents for epoxidation and anti-dihydroxylation
1. epoxidation: **MCPBA or RCO3H**
2. anti-dihydroxylation: **H3O+**
- adds 2 OH groups across the double bond in an anti fashion
87
difference in reagents between oxymercuration and ALKoxymercuration
oxymercuration using HgOAc and water
alkoxymercuration uses HgOAc and ROH (like CH3OH) - adds the alkoxy group (OR-)
*both are maokovnikov and anti addition though*
88
difference between halogenation of alkenes and halohydrin formation
**halogenation**: uses halogen in inert solvent (like CCl4 or CH2Cl)
**halohyrin formation**: uses halogen in non-inert solvent (like H2O or ROH - alcohol)
- product results in 1 halogen and 1 OH molecule put across the double bond
*both are anti addition because the attack is on a sp3 carbon since they both have the bromonium ion (3 membered ring) as an intermediate*
89
difference in product when using reagent KMnO4 in cold/dilute in basic medium verses hot/conc in acidic medium
**KMnO4 (hot, conc.) in H3O+**: permanganate cleavage of alkenes
- results in *ketone + carboxylic acid*
*think that heat can break through bonds*
**KMnO4 (cold, dil.) in NaOH**: syn-dihydroxylation
- results in 2 OH groups put across molecule in *syn addition*
*think that if you're cold you can break ice into 2 parts*
90
oxidative cleavage of alkenes: the 2 different types of reagents and what they're products are
both parts use **O3 (ozone)** in step 1
but second step can either be **reducing or oxidizing**
**reducing**: *Me2S/DMS or Zn, H2O, AcOH*
- results in formation of ketone and aldehyde when the bond is cleaved in half
**oxidizing**: *H2O2 (peroxide)*
- results in ketone + carboxylic acid (b/c the aldehyde gets oxidized further and cannot stay in aldehyde form turning into carboxylic acid)
91
which reaction mechanism forms the intermediate of the 4 membered ring with partial bonds?
hydroboration-oxidation
92
if the enantiomeric excess of a mixture if 50% what does that mean?
50% of the mixture consists of the (+) enantiomer (the excess) and the other 50% consists of the racemic form
- formula: (observed rotation/rotation of pure) x 100 or (major-minor/total) x 100
93
in hydride shifts is it possible to have a product without the hydride shift
yes, it is possible though it is rare
94
how to ensure alkylation of an acetylatide anion?
they undergo SN2 so:
- only use **primary alkyl halides** (tertiary and secondary are prone to elimination)
- avoid **protic solvents** (which protonate the anion)
- no **poor electrophiles (like vinyl or aryl halides)**
95
which alkenes are the most reactive toward acid-catalyzed hydration?
**the ones that form the most stable carbocation**
- when double bond is removed by the addition of the H, carbocation is formed so want the *most stable carbocation intermediate*
96
preparation of **acetylide ions** and how do they react?
to prepare: simply use **NaNH2 only (without reprotonating) in liquid NH3**
**reaction**:
- with primary or methyl substrates, *lead to substitution reactions* = synthesis of bigger alkynes (form carbon carbon bond making the chain longer)
- *in absence of chiral catalyst, addition to aldehydes and ketones will result in racemic mixture of 2 enantiomers*
- with 2º or 3º substrates, undergo E2 ELIMINATION (product is alkyne with leaving group separate and the newly formed alkene separate)
97
diemthyl sulfoxide
DMSO
98
Pcl5 with ketone
Forms geminal dihalide (basically take the =O and replace with 2 chlorine atoms)
