Alkyne Hydrogenation: Catalytic Conditions

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Hi friends! I finally got around to finishing the notes for this guide today! I would’ve posted yesterday but I was stuck at the hospital for around seven hours, so I was extra exhausted. Lowkey should’ve slept in more haha but it’s all good. 

So with these alkyne reactions, a lot of them are just repetitions of the alkene reactions covered in the previous guides. I would definitely refer to the mechanisms in the first guide, since the mechanisms are a lot more structured there. Some of the vocabulary here is reviewed in the second guide as well :)

Alkyne Hydrogenation: Catalytic Conditions

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H2, Pd/C is a reagent used in organic reduction and results in with syn hydrogenation

Catalytic conditions refer to how H2, Pd/C is a catalyst 

This reagent is used in 2 equivalents, which is why this reaction goes from alkyne to alkane

Alkyne Hydrogenation: Stop at Alkene 

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Sometimes we don’t want the alkyne to end up as an alkane. Rather, we want the product to be an alkene

That’s where Lindlar’s catalyst comes in, which is “poisoned” to prevent the alkyne from becoming an alkane 

Lindlar’s catalyst: Pd/BuSO4, quinoline, CH3OH

H2 and Lindlar’s catalyst prefers syn hydrogenation (aka cis alkene)

To get the trans alkene, just use Na (metal), NH3 (liquid) (or opt for Li metal)

Electrophilic Additions: Addition of HX

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HX is used twice to go from alkyne to alkene to alkane (thus excess HX)

X refers to the halogens Br, Cl, and I

This reaction follows Markovnikov’s rule, where X is added to the MORE substituted carbon

The product here is a geminal dihalide: both halogens on the same carbon

Electrophilic Additions: Addition of X2

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X2 is added twice to go from alkyne to alkane (thus excess X2)

Note that I2 wouldn’t work here

Markovnikov regioselectivity

Anti stereospecificity (aka anti-addition)

The product here is a vicinal dihalide: halogens on adjacent carbons

Alkyne Hydration: Oxymercuration 

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Note that we don’t have demercuration in alkyne hydration

The reagents are H2O, H2SO4 with either HgSO4 or Hg(OAc)2 the as catalyst

The product here is shown in the keto form, but in the enol form the OH would attach onto the MORE substituted carbon, thus Markovnikov regiochemistry

Alkyne Hydroboration/ Oxidation

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The product has “anti Markovnikov” regiochemistry, because the doubled-bond O attaches onto the LESS substituted carbon in the keto form (in the enol form, the OH attaches onto the less substituted carbon)

The reagents are BH3, THF and H2O2, OH

Keto-Enol Mechanism 

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Tautomers: structural isomers differing only in the position of an H

Enol and keto forms

Essentially, the OH in the enol form becomes a double-bonded O in the keto form

This is used with H3O+ as the initial electrophile and H2O as the second nucleophile (note that the forms change with the equilibrium reaction)

Resonance structures are formed between the enol and keto forms 

The examples featured underneath are condensed mechanisms of the oxymercuration and hydroboration/oxidation reactions featured above. We’re familiar with the enol forms (as seen in the alkene reactions), but the keto forms are drawn more often

Carbon Nucleophiles

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With carbon nucleophiles, you’re changing the carbon skeleton of the starting material

The reagents for this are Na+ and NH2- in the solvent NH3 (liquid)

The second step is the tricky part, because you have to come up with a reagent that establishes the new carbon-carbon bond shown in the product

Often times, I usually have to work backwards, meaning that the product is shown, so I need to figure out what that second reagent is

I do this by comparing the starting material and product to see what the new carbon-carbon bond(s) are 

Then, I’ll draw the new bond(s) in the second reagent and then add an extra bond with a good leaving group (think SN2 reaction!)

So when the leaving group leaves, the resulting positive charge is attracted to the negative charge of the carbon nucleophile

And BAM, a product with a new carbon skeleton!

It’s so important to number your carbons for these reactions!!

I hope this helped!! And again, please feel free to add more to this and/or make edits if I made a mistake. Thank you!! <3

More Posts from Ohkaydeh and Others

8 years ago

Tips on getting shit done a few days before the exam

Count the number of days left till the exam.

Count the number of topics you need to learn/revise before the exam.

Divide the number of topics by the number of days (you may reserve one or two days for the final revision). This is the amount of work you have to do per day.

Schedule your tasks every day from the time you wake up to the time you go to bed. Try to calculate as realistically as possible the amount of time you would need for each task (I like using Sectograph app for that).

Reserve 1-3 extra hours at the end of every day because you’re not gonna fit everything into the timetable anyway. Believe me.

Don’t forget to schedule some time for rest as well. Once more, be realistic.

Alternate your tasks throughout the day as much as possible. Don’t study the same subject or topic longer than a few hours.

Don’t forget to leave some time for meals, showering, social media and maybe even a film or two.

Just do stuff.

Don’t panic, you’ll get through that.

2 years ago

My Notion Set-Up

My Notion Set-Up
My Notion Set-Up
My Notion Set-Up
My Notion Set-Up
My Notion Set-Up
My Notion Set-Up

(from my IG)

4 years ago

dark academia: stem edition

the sense of roughness creeping onto your fingertips when the ball pen crashes with shabby loose-leaf paper.

the brightness of the laboratory making your eyes aware of something that you wish you could just grab and look at. something more than an idea. you try to wrangle the secrets out of the universe. and your tongue is bitter when you’re asked to leave before your experiment is done.

the stabbing pain that descends upon you when your mind runs off with little fuel, in a direction the yellow pencil in your hand can’t trace. your system is in chaos: you understand what entropy is. you exist, in a state of growing disorder.

the clear sense of belonging that crawls over you when you realize its 12 am and you’re still stuck in the library with nothing to show for but a completed lab report, with diagrams that weren’t required for credit but you couldn’t help but pour over the workings of the pulley with each force labeled to bits. the force of gravity is sinful, you enjoy how it makes the world turn, but sometimes, you wish it would let you fly.

the almost silent moment of calmness that fills your veins when you think of something broken in this world and your hands draw upon your mind like you cannot wait to fill this existing rupture. 

you are now a cosmic entity, and your data ignites ideas, and ideas ignite you, and every inch of you can’t help but wonder at what equation you must write and what flowchart you must draft. you are here to correct what must be a slight in the blueprint of the universe.

3 years ago
My Sanctum Where I Study,contemplate And Exist ..🏹

my sanctum where I study,contemplate and exist ..🏹

4 years ago

dark academia: stem + medicine

math: solving problems in the middle of the night, equations are written on the windowpane, quick calculations in your head, seeing mathematics as a secret language and barrier from the rest of the world, using probability theory to present a person’s life before their very eyes, understanding the algorithms governing every single step of „fate“ and how to manipulate them for your favor, cryptic notebooks, and lost alleyways

engineering: the power to create something that surpasses that is more than humans will ever be, governing and shaping the future of a whole civilization, late-night philosophizing on the nature and difference between humans and machines, crammed study sessions and tired blood-shot eyes

biology: extensive knowledge about herbology and toxicology, knowing almost every plant-based toxin and toxic mushroom in the local area, midnight at the lab with lowlights on and the dark hallways shrouded in mystery, glancing white lab-coats from the corner of your eye

chemistry: spending hours upon hours alone in the lab, perfecting formulas and conducting research because you just know the breakthrough is so close, sudden heureka moments in the middle of the night, inhaling new substances at secret meetings in old buildings to reach a state no human has reached before, prolonged shared eye contact and knowing smiles, the sound of a pen hastingly scribbling chemical formulas into a notebook

physics: „after all, murder is just the redistribution of matter, and matter is my specialty“, pointing out constellations in the sky, seeing patterns no one has seen before, wearing black turtlenecks and long coats while discussing quantum mechanics, hushed whispers, the melancholy of the endless search for another inhabitable planet, coffee cups left on the window sill

comp sci: the sound of typing at lightning speed, a lone screen glowing the absolute dark, losing track of time as you completely lose yourself in your code, trying again and again and again until it finally works, absolute dedication, crafting algorithms that can be used for good – but also for evil, code marathons isolating you from the rest of the world, being able to change lives at the press of a button

medicine: death looms always an inch too close, becoming as natural as life, white coats looming over the dissection table, staring at Rembrandt’s „the anatomy lessons of dr. nicholaes tulp“ in absolute awe, gloves covered in blood, syringes and needles in hand, hollowed laughter, being the last one in the library, knowing too well what sacrifice means

3 years ago
“I Wish You To Know
“I Wish You To Know
“I Wish You To Know
“I Wish You To Know

“I wish you to know

that you have been the last dream of my soul.”

—Charles Dickens, A Tale of Two Cities

4 years ago

stem in chaotic academia!!

(science & chemistry focus!)

quickly jotting down calculations with a pen and smearing ink all over your hand

very uneven, unsymmetrical benzene rings

having a used, marked up periodic table hanging by your desk even though you’ve practically memorised it

writing in pen and having to hastily scratch out errors because you have no time for correction tape (youre on the verge of discovery!)

having a favorite element

wearing your lab coat and safety goggles out by accident

chipped black nail polish on trimmed nails with only a choker and stud earrings for jewelry

having a worn out lab notebook, with a scruffed up cover and ink saturating the pages with your scientific knowledge

tacking anatomical diagrams from your textbook on the wall. or even better, drawing your own diagrams

secretly or not so secretly wanting to drink out of a (clean, not used in lab) beaker

taking lab safety seriously but also wanting to digest beautifully colored solutions because pretty

using up so many pens because of how much you write and calculate and document

notes in blue ink, bromophenol blue to be exact

knowing your polyatomic ions, constants, conversions and equations by heart but forgetting to round to the appropriate significant figures

highly corrosive substances

getting used to the smell of methane

treating the lab like your second home

euphoria brought on by being on the brink of discovery

trial, error, success and failure

loving what you do, what you study, and what you learn with all your heart

3 years ago

Having trouble developing the plot of a story? You aren’t alone—this is no small task. But that doesn’t mean it’s impossible. This guide is here to help.

So What Is the Plot of a Story?

Plot is the sequence of events that makes up your story. It’s what compels your reader to either keep turning pages or set your book aside.

Think of Plot as the engine of your novel.

A successful story answers two questions:

1. What happens?

2. What does it mean?

What happens is your Plot.

What it means is your Theme.

3 years ago
My Masterpost | My Studygram | Ask Me Anything
My Masterpost | My Studygram | Ask Me Anything
My Masterpost | My Studygram | Ask Me Anything
My Masterpost | My Studygram | Ask Me Anything

my masterpost | my studygram | ask me anything

[click images for high quality]

[transcript under the cut]

Other advice posts that may be of interest:

All About Procrastination

How To Study When You Really Don’t Want To

Common Study Mistakes

7 Strategies to Improve Concentration

Keep reading

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ohkaydeh - ohkaydeh
ohkaydeh

Math Enthusiast. Wanna be Doctor. Try'na be productive.

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