1) Three types of elimination reactions are α-, β-, and γ-elimination which involve the loss of atoms or groups from the 1st, 2nd, and 1st/3rd positions respectively of an organic molecule.
2) The mechanisms of elimination reactions can be E1 or E2. E1 involves carbocation intermediate while E2 is concerted. Kinetic studies can determine the mechanism.
3) Factors like nature of alkyl halide, base, and solvent determine if the reaction follows E1 or E2. E2 is favored with strong base and polar aprotic solvent.
Colorimetry is "the science and technology used to quantify and describe physically the human color perception".[1] It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space tristimulus values and related quantities.[2]
The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism.
The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism.
B.phram
Semester .4
Subject : Organic chemistry - III
Use as reference and also usable for examination prearation.
gtu afflitited phramacy college's student may using this ppt.
PPT Describe elimination reactions, Evidences and mechanism of elimination reaction. Energy profile diagram. RELATIVE stabilities of intermediates. Comparison between E1 & E2 elimination reaction
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Colorimetry is "the science and technology used to quantify and describe physically the human color perception".[1] It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space tristimulus values and related quantities.[2]
The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism.
The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism.
B.phram
Semester .4
Subject : Organic chemistry - III
Use as reference and also usable for examination prearation.
gtu afflitited phramacy college's student may using this ppt.
PPT Describe elimination reactions, Evidences and mechanism of elimination reaction. Energy profile diagram. RELATIVE stabilities of intermediates. Comparison between E1 & E2 elimination reaction
Pulmonary Thromboembolism - etilogy, types, medical- Surgical and nursing man...VarunMahajani
Disruption of blood supply to lung alveoli due to blockage of one or more pulmonary blood vessels is called as Pulmonary thromboembolism. In this presentation we will discuss its causes, types and its management in depth.
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Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
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Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
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The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
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disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
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effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
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June 20, 2024, Prix Galien International and Jerusalem Ethics Forum in ROME. Detailed agenda including panels:
- ADVANCES IN CARDIOLOGY: A NEW PARADIGM IS COMING
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- WHAT’S NEW IN THE TREATMENT OF INFECTIOUS,
ONCOLOGICAL AND INFLAMMATORY SKIN DISEASES?
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2. Three major types of elimination reactions are:
1) α-elimination: two atoms or groups are removed from the
same atom. It is also known as 1,1-elimination.
2) β-elimination: loss of atoms or groups on adjacent atoms.
It is also known as 1, 2- elimination.
3) g-elimination: loss of atoms or groups from the 1st and 3rd
positions as shown below.
3.
4. The Mechanisms of Elimination
What is the mechanism for elimination?
What is the order of bond breaking and bond making?
Is the reaction a one-step process or does it occur in many steps?
There are two mechanisms for elimination—E2 and E1
The E2 and E1 mechanisms differ in the timing of bond cleavage
and bond formation.
5.
6. Figure 5.1. An energy diagram for an E2 reaction:
(CH3)3CBr + –OH → (CH3)2C═CH2 + H2O + Br–
7. E2 reactions are generally run with strong, negatively charged bases like
–OH and –OR.
Two strong, sterically hindered nitrogen bases, called DBN and DBU,
are also sometimes used.
DBN=1,5-diazabicyclo[4.3.0]non-5-ene,
DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.
There are close parallels between the E2 and SN2 mechanisms in how the
identity of the base, the leaving group, and the solvent affect the rate.
8.
9. Because polar aprotic solvents like (CH3)2C═O do not solvate anions well, a
negatively charged base is not “hidden” by strong interactions with the solvent,
and the base is stronger.
Then, a stronger base increases the reaction rate.
10. Why does increasing alkyl substitution increase the rate of an E2 reaction?
In the transition state, the double bond is partially formed, so increasing the
stability of the double bond with alkyl substituents stabilizes the transition state.
11. The Zaitsev Rule
A mixture of alkenes can form from the dehydrohalogenation of
alkyl halides having two or more different β carbon atoms.
When this occurs, one of the products usually predominates.
The major product is the more stable product—the one with the more
substituted double bond─Zaitsev Rule
A reaction is regioselective when it yields predominantly or exclusively one
constitutional isomer when more than one is possible.
E2 reaction is regioselective
12. Exception:
The less stable alkene is the major product if the base in an E2 reaction is
sterically bulky!
The bulky base picks easily accessible proton and less substituted alkene is
formed predominantly.
13. When a mixture of stereoisomers is possible from dehydrohalogenation,
the major product is the more stable stereoisomer-trans alkene.
A reaction is stereoselective when it forms predominantly or exclusively
one stereoisomer when two or more are possible.
The E2 reaction is stereoselective because one stereoisomer is formed
preferentially.
14.
15.
16. Figure 5.2: Energy diagram for an E1 reaction:
(CH3)3CI + H2O(CH3)2C═CH2 + H3O+ + I–
17. Increasing alkyl substitution has the same effect on the rate of both an
E1 and E2 reaction; increasing rate of the E1 and E2 reactions:
RCH2X (1°) <R2CHX (2°) < R3CX (3°).
19. 5.2. Evidences for mechanisms of elimination reaction
Evidences for E2 mechanism
1) There is kinetic isotopic effect
2) Kinetic data shows second order kinetics
3) There is no rearrangement
21. This clearly indicate that in E2 elimination, breaking of Cβ-H bond must
occurs in the slow step (RDS).
22. Kinetic study shows that doubling the concentration of one reactant
doubles the rate of the reaction and
Doubling the concentration of both reactants increases the reaction rate
by a factor of four.
This indicate that the rate of the reaction depends on the concentration
of both reactants (both of them appear in the RDS).
Therefore, it exhibits second order kinetics & must follow E2
mechanism.
2) Kinetic data shows second order kinetics
3) Absence of rearrangement:
indicates that the reaction doesn’t involve carbocation formation and
therefore it occurs through E2 mechanism.
23. 1) No kinetic isotopic effect
2) Kinetic data shows first order kinetics
3) There is rearrangement
Evidences for E1 mechanism
24. 5.3. El versus E2
1) When Is the Mechanism E1 or E2?
This depends on the nature of alkyl halide, the base & the solvent.
Primary alkyl halides undergo only E2 elimination reaction.
They can not undergo E1 reaction.
For those alkyl halides that can undergo both E2 and E1 reactions (i.e. 1o&2o)
E2 reaction is favored by a high concentration of a strong base and
polar aprotic solvent (e.g., DMSO or DMF).
E1 reaction is favored by a weak base and a polar protic solvent
(e.g.,H2O or ROH).
25. Predicting the substitution and elimination products of a reaction can then
be organized by the type of alkyl halide, as shown in the following table.
5.4. Elimination versus substitution
How do we know if a given alkyl halide will undergo substitution or
elimination with a given base or nucleophile, and by what mechanism?
To determine the product of a reaction with an alkyl halide:
26.
27.
28.
29. Exercise:
Draw the products of the following reaction, and include the mechanism showing
how each product is formed.
A)
B)
C)
30. 5.5. Applications of elimination reactions
A) Dehydration of alcohols: Synthesis of alkenes
31.
32.
33. Dehydration follows Zaitsev’s rule
This depends on carbocation stability
This depends on alkene stability
30 alcohols dehydrate easily.
35. A very strong base such as -NH2 or K+ -OC(CH3)3 in DMSO is needed for the
second elimination since vinyl halide intermediate is less reactive.
If a weaker base, the reaction will stop at the vinylic halide and no alkyne will
be formed.
Vicinal dihalides can undergo two consecutive E2 dehydrohalogenations,
giving alkynes.
B) Dehydrohalogenation of Vicinal Dihalides: Synthesis of alkynes
36. C) Hofmann Elimination: Synthesis of alkenes
The reaction of a quaternary ammonium ion with hydroxide ion is known as a
Hofmann elimination reaction.
The leaving group in a Hofmann elimination reaction is a tertiary amine.
A Hofmann elimination reaction is an E2 reaction.
37. Regiochemistry of Hofmann Elimination
The less substituted alkene is the major product (anti Zaitsev’s rule)!
Why do quaternary amines violate the rule?
Steric factor is the main reason (bulky leaving group).
Steric factor in the Hofmann reaction favors anti-Zaitsev’s product.
38. D) Acetate pyrolysis: Synthesis of alkene
Is heat induced intramolecular syn-elimination of acetate ester with β-
hydrogen to form alkene product.
A concerted reaction via a cyclic transition state.
An intramolecular proton transfer is accompanied by syn-elimination to form
a new carbon-carbon double bond.
The carboxylic acid corresponding to the ester is a byproduct.
39. If more than 1 β hydrogen is present then mixtures of alkenes are generally
formed.
The loss of the β-hydrogen occurs preferably from the most unhindered
position (Acetate pyrolysis obeys Hofmann rule).
40. E) Cope elimination reaction: Synthesis of alkenes
Amine oxides undergo a reaction similar to the Hofmann elimination
reaction, called a Cope elimination reaction.
Intramolecular E2 reaction.
Major product of Cope elimination is like that of the Hofmann elimination.
41. F) Applications of elimination reaction in drug synthesis & metabolism
E2 reaction is used in the synthesis of quinine, a naturally occurring antimalarial
drug.
Bonds and atoms in quinine that originate in
the alkene intermediate are shown in red.
42. Atracurium (muscle relaxant drug)- useful during surgery when the
patient needs to be immobilised.
The effect of such drugs should be wear off after surgery and unless it
can cause respiratory depression.
The effect would only wear off after the drug gets metabolised – that is it
gets changed in the body – to a not active form.
One such change involves an elimination reaction of the quarternary
ammonium group of the drug.
Elimination reaction in drug metabolism.