#homolytic

[the-queen-of-today]

[materialsscienceandengineering]

A new design strategy for mechanoresponsive materials with high thermal tolerance

In recent years, scientists have developed a wide range of smart materials known as "mechanoresponsive materials" (MRMs), which exhibit fluorescence, coloring, self-healing, and even self-strengthening in response to mechanical stimuli. One such class of materials is mechanophores—molecules that can undergo small-scale chemical reactions upon exposure to a mechanical stimuli—which are being extensively studied due to their potential application in the fabrication of highly functionalized polymers. For instance, radical-type mechanophores (RMs) can undergo mechanical stimuli-induced homolytic scission or breaking of the central carbon–carbon (C–C) bond. Studies have shown that the nature of the C–C bond often decides the heat tolerance, self-healing, chemical reactions for polymeric material preparation and ambient temperature handling of the resulting polymer materials. To improve the reliability of RMs, it is necessary to ensure high stability under thermal stimuli while retaining their mechanical responsiveness. However, there is a lack of rational design strategies for the synthesis of novel RMs.

Read more.

[puzzlehat]

okay so the wifi i'm on right now is shitting itself despite this being a popular study spot on campus but REGARDLESS i'm studying for my third organic chemistry midterm right now (my class grade is a 90.2% so i'm barely hovering around an A and i'd REALLY like to keep it that way as unrealistic as that may be) and as much as i am absolutely loving this class i'm struggling a little with remembering all of the mechanisms (final exam review sheet posted by professor indicates 40 different reactions we need to know).

granted, a lot of them share the same patterns, but i don't know what format i'll need to compare-contrast all of them in in order to have them down pat for may 2. so right now i'm just focusing on this exam, where we've gotta know

radical substitution of alkanes and allylic substitution, the funky alkyl halide ones with the fishhook arrows. the simplified mechanism looks like halogenation except these are done with heat/light. these go through three stages: initiation from nonradical to radical, propagation from radical to radical, and termination from radical to nonradical. you get your radical intermediate via homolytic cleavage, you react it with a hydrogen coming off of the most substituted carbon, you get your next radical intermediate once the hydrogen is gone, you react all your radicals together to tie things up nicely. if your radical is on a carbon that neighbors a double bond, you have a nice stable allylic radical (thank you resonance), but if your radical is on a double bond, that's a vinyl radical and we don't like those... you also gotta pay attention to where your alkene is because that'll affect your stability too. if you're happening to do your reaction with peroxides, you'll be reacting your intermediate with the less substituted area. a halogen? on MY terminal end?

elimination and substitution reactions Sn1/Sn2/E1/E2. these are silly and complicated and i need to make a chart to understand them better, but the substitution reactions will substitute a nucleophile in for the leaving group, and the elimination reactions will make an alkene out of an alkane using a base, and the 2-reactions are concerted with steric barriers while the 1- reactions have a carbocation intermediate with stability as the barrier.

alkyne reactions, including deprotonation (basically acid-base shit), alkyne formation (using acetylene, which makes good internal alkenes and looks like Sn2, or dibromides, which looks like two E2 reactions and can be done with bromides on the same carbon or on adjacent carbons), halogenation (nonregioselective concerted anti-addition of halogens using Br2/Cl2), hydrohalogenation (markovnikov addition of Br, can happen twice if you have two equivalents of HBr, carbocation intermediate), hydration and hydroboration-oxidation (markov and anti-markov reactions, respectively; adding a hydrogen and an OH, keto-enol tautomerism where you end up with the double bond on the oxygen), and three reduction reactions (Pd/C yields alkane, Lindlar/H2 yields a cis(z)alkene, Na/NH3 yields a trans(E) alkene).

anyway i have practice problems to do and the sn1/sn2/e1/e2 reaction comparison chart to make but i'm drinking my first monster energy (ultra paradise. it's good) and i'm getting dinner w at least one of my friends in 25 minutes... calc homework still due tonight but i think i'll be able to get it... exam in 3 hours... feeling good!

[suprimacottonsblog]

Top Mercerized cotton Secrets

09 Jun 2018 I would like you’d do a crotchet along tutorial with photos demonstrating tips on how to crochet comprehensive that adorable green bag you exhibit to the e-newsletter advertising and marketing this post. I'd so like to make it but I don’t understand how to go through crochet Recommendations. I discovered a filet crochet cowl but it took me quite a while to locate vids demonstrating me exactly what to complete. At this point the fiber is like a solid cylindrical rod acquiring a central lumen or canal pointing towards the suggestion consisting solely of cellulose. Once the boll bursts and exposes these fibers to sun and air they dry up and collapse, turning out to be flatterand ribbon like with alternating remaining and appropriate spiral twist just about every two or three turns. This really is cotton fiber in its primary condition. Furthermore, nearly anything metallic could potentially cause the product to burn or destruction the microwave. So, if you're constructing your incredibly hot pad or bag, you should definitely only use pieces which will get up to repeated use inside the microwave. Mercerizing generally imparts quick treatment properties to cotton fabrics, significantly when made use of together with other finishes. That said, some mercerized yarns and threads can arrive out of your clean feeling rigid, which may be discouraging In relation to clothes such as shirts and sweaters. The conversation from the Energetic species of the plasma with cellulose (along with other polymer) surfaces, will involve a number of electron-mediated processes, and good ion-induced reactions. Many of these reactions can encourage homolytic bond cleavages bringing about the development of absolutely free-radical internet sites. These reactive centres may lead to a variety of functionalisation mechanisms, determined by where from the cellulose composition They can be designed. Free radical web-sites ordinarily consist of unpaired electrons which aren't linked to chemical bonding, which establishes their exceptionally high instability and high reactivity. Being a consequence, free of charge mercerized cotton radicals generated on a polymer surface, e. You should enter a legitimate email handle. Seems like you already have an account! You should Log in to subscribe. You've got presently signed up for a few newsletters, however, you haven't confirmed your deal with. Etsy is not supporting older versions of the Internet browser so as making sure that consumer data remains secure. Remember to update to the most recent Variation. For instance, the three Main features of the papermaker's felt are h2o removal, end, and electricity transmission. Drinking water removing is a vital factor because the improved the h2o removal, the more quickly the machine will run. The finish is equally crucial since the felt must be completely defect totally free; the slightest imperfection inside the area would leave a mark from the paper. The most significant aspect is electric power transmission. The entire press section is operate off of one drive roll. Some push sections are a few tales superior and pull lots of pulp within an aqueous point out by its cycle. Some call for a countless felt twenty five ft broad and 110 toes very long. Prolonged, great cotton threads are generally used for mercerization, including Egyptian and Pima cotton, as they involve much less twist than other fibers Utilized in the method. The entire process of generating mercerized cotton is very elaborate. Cotton fiber grows in a very boll; Just about every fiber is developed from a person seed (about 5,000 completely) in the bottom. The fiber begins out as being a projecting hollow sheath and every night a brand new layer of cellulose is laid down on The within of the sheath right until about 30 layers are built up. Element of mercerized cotton currently being stronger signifies it sacrifices softness. If you're earning a thing where strength of the fabric or structure is important than mercerized cotton might be a much better selection.

[dracademy]

General Organic Chemistry

General Organic Chemistry- General Organic Chemistry introduces students to the core concepts of organic chemistry. A solid comprehension of the principles covered by GOC is essential for studying more advanced topics.

General Components of an Organic Reactions- Organic reaction reactants are categorized as follows:

Reagents- Chemical species that cause a reaction by attacking another species. 

Substrate- In an organic reaction, the species that are attacked by a reagent.

The location of the reagent attack can differ depending on the type of the reagent-

Electrophiles- They are species that lack electrons and assault the substrate in an area with a lot of electrons.

Nucleophiles- They are species with lots of electrons that frequently give away their electrons. In general, nucleophiles attack the reagent at an area with low electron density.

In most chemical reactions, old chemical connections are broken and new ones are created. A covalent bond can break in one of two ways: homolytic fission creates species known as radicals, and heterolytic fission results in the production of an ion pair consisting of a positively charged cation and a negatively charged cation and negatively charged anion.

Inductive Effects- A carbon chain is transformed into a permanent dipole when an electron-deficient molecule is added. The difference in the electronegativities of the atoms in the molecule is what causes the dipole, which is why this effect is known as the inductive effect. Down the carbon skeleton, the partial charge's magnitude decreases. From the fourth carbon atom in the chain, its size can be avoided.The inductive effect is a long-lasting phenomenon that depends on distance and is transmitted via sigma bonds. Inductive effects can be divided into two categories: +I (raises acidity and reduces the basicity) and -I (reduces acidity and raises basicity).

Electromeric Effect- The whole transfer of pi electrons to one of the linked atoms in an organic molecule causes the electromeric effect. Because there is an attacking reagent present, it has a temporary effect.The electromeric effect disappears when the attacking reagent is removed from the system. There are two types of electromeric effects +E, the pi electron moves towards the attacking reagent when it is an electrophile, which then attaches to the negatively charged atom that still has the bond pair and -E, The pi electron shifts away from the attacking reagent when it is a nucleophile, which attaches to the negatively charged atom that lost its pi-electron.

Hyperconjugation- Adjacent sigma bonds that provide empty p-orbitals with electrons stabilize carbocations. Hyperconjugation is the term used to describe this impact, which is permanent. 

Mesomeric- The delocalization of electrons through a network of pi bonds is a component of the mesomeric effect. The polarity that emerges in organic compounds as a result of interactions between two pi bonds is caused by the mesomeric effect. Consequently, both negative and positive charges can be stabilized. Two different forms of mesomeric effects exist- +M, electrons are donated by a pi-system in this process, and they usually travel away from these groups, -M,Since electrons usually advance these groups, it involves a pi-system accepting electrons.

Resonance Effect- Pi-electrons and lone pairs over molecules are delocalized as a result of the resonance effect. As a result, various speculative molecular configurations called resonance structures are produced. Two distinct resonance effects exist: +R, it happens when a single pair of electrons enters a molecule, -R, It generally happens because of species that lose electrons or species with empty p or d orbitals.

Isomerism- Multiple compounds with the same chemical formula but different chemical structures are said to exhibit isomeric behavior. Isomers are the names for chemical substances that exhibit isomerism. Stereoisomerism and structural isomerism are the two different types of isomerism.

General Organic Chemistry is a vital topic of chemistry for NEET aspirants, it is as tough as well as important to clear NEET. To understand it better, everyone needs guidance from the Best NEET coaching in Bangalore, they provide notes, full guidance, PYQ, and mock tests for students to clear and strengthen their base for NEET and upcoming syllabus.

[theblessingep]

Homolytic bond cleavage

[lookchem]

767-58-8 The Photochemistry of Conformationally Rigid Benzylic Esters: 2,2-Dimethyl-1-indanyl Acetates and Pivalates

The photochemistry, in methanol, of substituted 2,2-dimethyl-1-indanyl acetates 9a-c and pivalates 10a-c has been studied.In agreement with previous studies on benzylic esters, the results show that the substituents change the yield of products derived from the ion pair.The mechanistic conclusion reached is that the substituents change the oxidation potential of the indanyl radicals and thus the rate constant of electron transfer for converting the radical pair to the ion pair.The results also reveal two other substituent effects.First, substituents can increase the overall efficiency of the photoreaction by enhancing homolytic cleavage.The second effect is conformational.In compounds where the bond that is cleaving is conformationally mobile, such as the C-O bond in benzylic esters, substituents on the ring can change the population of the reactive conformer and thus the overall efficiency of the reaction.For the indanyl acetate esters, the difference in excited-state reaction rate between the m- and p-methoxy substituted ester is 15:1.For the m- and p-methoxy substituted benzyl acetates, this difference in reaction rate is 48:1.The larger difference in reaction rate for the conformationally mobile benzylic esters is attributed to a higher population of the unreactive conformer for the p-methoxy substituted ester.

https://www.lookchem.com/CASDataBase_767-58-8.htm

[grocerystore-gf]

[me and my bestie studying chemistry] hm heterolytic cleavage and homolytic cleavage? capitalism and communism. what’s next

[hotchley]

Right so I know my 🌙 anon definitely does chemistry, but even if you don’t, listen to this because it’s hilarious.

There’s a thing called heterolytic and homolytic fission. What actually goes on is irrelevant, but you learn about it in organic chemistry right. Well me and my friend dubbed ourselves heterolytic and homolytic fission. Yesterday I made a joke about how we should get friendship bracelets that say heterolytic and homolytic fission on them.

Today she comes in with a bracelet she made for me. And it says heterolytic on it, and it’s blue, and they have a matching one that says homolytic, because our wrists are too small for the whole word.

And it’s just so cute!!

[redacted-metallum]

Briefly misread my organic chem textbook as saying "homophobic cleavage" instead of "homolytic cleavage"

[gaysie]

help girl they’re doing homolytic bond cleavage in my oxyanion hole

[mclean45036228-blog]

Examine This Report on air conditioning sydney

The troposphere finishes abruptly in the tropopause, which seems during the picture because the sharp boundary concerning the orange- and blue-coloured environment. The silvery-blue noctilucent clouds increase much previously mentioned Earth's troposphere.

The ozone layer is contained inside the stratosphere. In this layer ozone concentrations are about 2 to 8 elements for each million, which is Significantly increased than during the decreased environment but nonetheless incredibly tiny compared to the principle parts on the environment.

Air conditioning can make deep approach properties feasible, for normally they would need to be crafted narrower or with mild wells so that inner Areas received enough out of doors air by means of organic ventilation.

Because in a super gasoline of continuous composition the speed of seem depends only on temperature rather than about the gasoline stress or density, the speed of seem during the environment with altitude takes on the form on the challenging temperature profile (see illustration to the right), and isn't going to mirror altitudinal changes in density or stress. Density and mass

Air conditioning (generally generally known as AC, A/C, or air con)[1] is the process of taking away warmth and moisture from the inside of an occupied Room, to improve the comfort of occupants. Air conditioning can be used in both equally domestic and business environments.

[sixty one] As soon as the refrigerant reaches the stratosphere, UV radiation in the Solar homolytically cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine radicals catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from robust UV radiation. Each chlorine radical stays Lively like a catalyst right up until it binds with Yet another radical, forming a stable molecule and quenching the chain response.

"Sleeping porches are often uncovered on residences by bodies of water," states Hogg. "The air was so enjoyable during the evenings via the water that folks would need to slumber inside of a shielded Room outside the house."

The amount of oxygen during the environment has fluctuated throughout the last 600 million yrs, reaching a peak of about thirty% around 280 million yrs in the past, drastically increased than present-day 21%. Two primary processes govern changes during the environment: Crops use carbon dioxide in the environment, releasing oxygen. Breakdown of pyrite and volcanic eruptions launch sulfur into the environment, which oxidizes and that's why reduces the quantity of oxygen during the environment.

Air conditioning can also be provided by a procedure identified as cost-free cooling which employs pumps to flow into a coolant (generally water or simply a glycol blend) from a chilly supply, which consequently functions like a warmth sink with the Vitality that is removed from the cooled Room. Popular storage media are deep aquifers or simply a organic underground rock mass accessed by means of a cluster of tiny-diameter boreholes, Geared up with warmth exchanger.

This method also designed the air much more humid, that may be valuable inside of a dry desert local climate. In ancient Rome, water from aqueducts was circulated with the partitions of selected residences to cool them. Other strategies in medieval Persia associated the usage of cisterns and wind towers to cool properties during the hot time.[5]

The refractive index of air is near to, but just increased than 1. Systematic versions in refractive index may result in the bending of sunshine rays more than lengthy optical paths.

e., the temperature distribution with the geographical location on the SEER check). SEER is abnormal in that it's made up of an Imperial device divided by an SI device. The COP is actually a ratio While using the identical metric models of Vitality (joules) in both equally the numerator and denominator. They terminate out, leaving a dimensionless amount. Formulas with the approximate conversion concerning SEER and EER or COP can be found.[34]

Since the title implies, the composition of a sleeping porch is very much just like a balcony—consider it like a three-time sunroom, in a sense. An excellent instance is in the Gamble Residence, an Arts & Crafts mansion in Pasadena by Greene and Greene, finished in 1910.

Early twentieth century awning advertisements describe the advantages of awnings in an analogous method to that of air conditioners: “Awnings generally lessen the temperatures and lessen the glare,” states just one 1909 advertisement. “The scorching rays on the sun is likely to make you hurry and bustle when real summer time climate strikes the city. Improved have your awnings designed and put up, then when you really want them they’re Prepared,” states Yet another. https://www.teknicoolairconditioning.com.au/services/ https://gholson71745454.wordpress.com/2019/02/15/considerations-to-know-about-air-conditioning-sydney/ https://llas33782667935.tumblr.com/post/182833317690/little-known-facts-about-air-conditioning-sydney

[mocktopper]

Class 11 Chemistry Chapter 6 – Hydrocarbons

Class 11 Chemistry Chapter 6 – Hydrocarbons

Question 13.1: How do you account for the formation of ethane during chlorination of methane? Answer: Chlorination of methane proceeds via a free radical chain mechanism. The whole reaction takes place in the given three steps. Step 1: Initiation: The reaction begins with the homolytic cleavage of Cl – Cl bond as: Step 2: Propagation: In the second step, chlorine free radicals attack methane…

[as-studypeach]

Haloalkanes and Their Angelic Reactions: Part One

Haloalkanes are more commonly referred to as halogenoalkanes. Obviously you’ve already read my post on halogenoalkanes and their properties so there’s no surprise that you’re itching to read what I’ve got to say about these beauties and their reactions! Should we delve in?

There are a few different kinds of reactions you must learn for the A Level exam that involve halogenoalkanes. 

The first is the synthesis of chloroalkanes via the photochemical chlorination of the alkanes. I know it looks scary, but don’t worry, it is simpler than it sounds. It essentially means “forming chloroalkanes through chlorinating an alkane in the presence of sunlight”.

Chlorine will react with methane when UV light is present and will form several kinds of chloroalkanes and fumes of hydrogen chloride gas. Chloromethane was once commonly used as a refridgerant. Depending on how many chlorine molecules there are, there will be different compounds formed:

methane + chlorine -> chloromethane + hydrogen chloride

CH4 + Cl2 -> CH3Cl + HCl

or

methane + chlorine -> trichloromethane + hydrogen chloride

CH4 + 3Cl2 -> CHCl3 + 3HCl

When undergone in real life, mixtures of halogenoalkanes are produced with some long chain alkanes which can be separated out with fractional distillation. 

To understand what happens in an overall chemical reaction, chemists use mechanisms. These basically show the step-by-step process that is usually shown by a simple symbol equation that summarises everything.

The chlorination of methane is something you must learn the mechanism for. It’s pretty easy but involves a lot of steps and must be revised periodically to remember them.

The actual reaction is a substitution reaction because one atom or group is replaced by another. Since the chlorine involved is a free radical, it can also be called a free-radical substitution reaction.

1. Initiation

UV light is essential for the first step in the mechanism. This breaks the Cl-Cl covalent bond so that each chlorine leaves with one electron from the shared pair. Chlorine free radicals, with one unpaired electron in the outer shell, are formed. Free radicals are only formed if a bond splits evenly - each atom getting one of the two electrons. The name given to this is homolytic fission.

2. Propagation

This has two sub-steps

(a) Chlorine free radicals (highly reactive) react with methane to form hydrogen chloride and leave a methyl free radical.

Cl• + CH4 -> HCl + •CH3

(b) This free radical then reacts with another chlorine to form chloromethane and another chlorine free radical. Producing free radicals is a chain reaction which is why it is such a problem in ozone depletion - a little amount can cause a lot of destruction.

•CH3 + Cl2 -> CH3Cl +  •Cl

3. Termination

This step stops the chain reaction. It only happens when two free radicals collide to form a molecule in several ways:

Cl• + Cl• -> Cl2

UV light would just break down the chlorine molecule again, so although this is technically a termination reaction it is not the most efficient.

Cl• +  •CH3 -> CH3Cl

Forming one molecule of methane uses one chlorine and one methyl free radical.

•CH3 +  •CH3 -> C2H6

Ethane can be formed from two methyl free radicals - this is why there are longer chain alkanes in the mixture. 

This whole process is how organic halogenoalkanes are the product of photochemical reactions of halogens with alkanes in UV light - made via free radical substitution mechanisms in chain reaction.

Another reaction you need to know is a nucleophilic substitution reactions. A nucleophile is an electron pair donor or proton acceptor - the name comes from Greek origins (”loves nucleus”) - such as hydroxide ions, cyanide ions or ammonia molecules. Hydroxide and cyanide ions are negative but ammonia is neutral.

Halogenoalkanes have a polar bond because of the difference between the highly electronegative halogen and the carbon atom. The 𝛿+ carbon can go under nucleophilic attack. The mechanism for negatively charged nucleophiles these in general is:

Nu represents the nucleophile. This example is with a bromoalkane. Make sure to include curly arrows that begin at a lone pair or the centre of a bond and end at an atom or centre of bond, and delta (slight) charges.

Lets look at a more specific example:

One nucleophile that can be used is a hydroxide ion, found in either water or sodium hydroxide. In this case, you need to know about aqueous sodium hydroxide or potassium hydroxide and a halogenoalkane. This takes place at room temperature but is slow so is often refluxed (continuously boiled and condensed back into the reaction flask). Reflux apparatus is shown below:

The halogenoalkane is dissolved into ethanol since it is insoluable in water and this solution along with the aqueous hydroxide can mix. The product produced is an alcohol, which is organic.

The general reaction is:

R-CH2X + NaOH -> CH3CH2OH + NaX

Where X represents a halogen.

You must learn the mechanism for this reaction. The lone pair on the hydroxide attacks the carbon atom attached to the halogen and this causes both carbon electrons to move to the halogen which becomes a halide ion.

The reaction of a hydroxide ion can also be classed as a hydrolysis reaction as it breaks down chemical bonds with water or hydroxide ions. The speed of reaction depends on the strength of the bond - a stronger carbon-halogen bond, a slower reaction.

C-I is the most reactive (reactivity increases down group 7) and C-F is therefore the least reactive and strongest.

Part two of this post will cover nucleophilic substitution of cyanide ions and ammonia molecules, as well as elimination reactions.

SUMMARY

You need to know about the synthesis of chloroalkanes via the photochemical chlorination of the alkanes. - “forming chloroalkanes through chlorinating an alkane in the presence of sunlight”.

Chlorine will react with methane when UV light is present and will form several kinds of chloroalkanes and fumes of hydrogen chloride gas. Depending on how many chlorine molecules there are, there will be different compounds formed.

When undergone in real life, mixtures of halogenoalkanes are produced with some long chain alkanes which can be separated out with fractional distillation. 

To understand what happens in an overall chemical reaction, chemists use mechanisms. These basically show the step-by-step process.

The chlorination of methane is something you must learn the mechanism for. The actual reaction is a substitution reaction because one atom or group is replaced by another. 

The first step is initiation - UV light is essential for the first step in the mechanism. This breaks the Cl-Cl covalent bond so that each chlorine leaves with one electron from the shared pair. Chlorine free radicals, with one unpaired electron in the outer shell, are formed. Free radicals are only formed if a bond splits evenly - each atom getting one of the two electrons.

Step two is propagation: (a) Chlorine free radicals (highly reactive) react with methane to form hydrogen chloride and leave a methyl free radical (b) this free radical then reacts with another chlorine to form chloromethane and another chlorine free radical. Producing free radicals is a chain reaction which is why it is such a problem in ozone depletion - a little amount can cause a lot of destruction.

To stop the chain reaction, the final step is termination. It only happens when two free radicals collide to form a molecule in several ways: two chlorine free radicals forming a chlorine molecule, two methyl FRs forming ethane or a chlorine FR and a methyl FR forming chloromethane.

Ethane contributes to the longer chain alkanes in the mixture. 

Another reaction you need to know is a nucleophilic substitution reactions. A nucleophile is an electron pair donor or proton acceptor, such as hydroxide ions, cyanide ions or ammonia molecules. Hydroxide and cyanide ions are negative but ammonia is neutral.

Halogenoalkanes have a polar bond because of the difference between the highly electronegative halogen and the carbon atom. The 𝛿+ carbon can go under nucleophilic attack. 

Nu represents the nucleophile. Make sure to include curly arrows that begin at a lone pair or the centre of a bond and end at an atom or centre of bond, and delta (slight) charges.

One nucleophile that can be used is a hydroxide ion, found in either water or sodium hydroxide. In this case, you need to know about aqueous sodium hydroxide or potassium hydroxide and a halogenoalkane. This takes place at room temperature but is slow so is often refluxed (continuously boiled and condensed back into the reaction flask). The halogenoalkane is dissolved into ethanol since it is insoluable in water and this solution along with the aqueous hydroxide can mix. The product produced is an alcohol, which is organic.

The general reaction is :R-CH2X + NaOH -> CH3CH2OH + NaX where X represents a halogen

The lone pair on the hydroxide attacks the carbon atom attached to the halogen and this causes both carbon electrons to move to the halogen which becomes a halide ion.

The reaction of a hydroxide ion can also be classed as a hydrolysis reaction as it breaks down chemical bonds with water or hydroxide ions. 

The speed of reaction depends on the strength of the bond - a stronger carbon-halogen bond, a slower reaction. C-I is the most reactive (reactivity increases down group 7) and C-F is therefore the least reactive and strongest.