Conversely, acidity in the haloacids increases as we move down the column.
In order to make sense of this trend, we will once again consider the stability of the conjugate bases. Because fluorine is the most electronegative halogen element, we might expect fluoride to also be the least basic halogen ion.
But in fact, it is the least stable, and the most basic! It turns out that when moving vertically in the periodic table, the size of the atom trumps its electronegativity with regard to basicity. The atomic radius of iodine is approximately twice that of fluorine, so in an iodine ion, the negative charge is spread out over a significantly larger volume:
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Re: ascorbic acid
curvedarrowpress.com/wpblog/?p=128
Ascorbic acid is a good problem to examine.
I really like this example. It is data. I do not doubt the values.
Because organic chemistry is really about electron movements, it is always intriguing to learn about how and what factors result in their movement and effects.
Ammonia is an inductive electron withdrawing group to form an amide anion, but a resonance donating group in aniline.
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What should the values for ascorbic acid be?
Image may be NSFW. Clik here to view.Acetoacetate is about 11, acetylacetoneImage may be NSFW. Clik here to view. is about 9, 3-oxobutanal is about 6, dimedone is about 5.
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Image may be NSFW. Clik here to view.I drew 3-oxobutanal as 4-hydroxybut-3-en-2-one as I believe that is its predominant form.
This is the vinylogous acid I was originally noting. In that instance, I was arguing that although a greater number of resonance structures can be drawn for the anion, its pKa was less than a carboxylic acid.
Even though resonance exists, separating the OH group from the more electron withdrawing C=O results in lower acidity. I think increasing conjugation will make an enol/aldehyde behave more like an isolated enol-aldehyde.
Why is ascorbic acid more acidic than dimedone or acetoacetate and which OH is more acidic?
As pointed out, it could have been either one. “A” is closer to the electron withdrawing C=O group. “B” bears the resonance effect noted earlier.
What if there wasn’t a “B”-OH?
Which carbon of an enone is more electron deficient?
The beta carbon is. Is this resonance or inductive? It actually is both. The electrons can interact to deliver the pi-electrons toward the carbonyl group.
Because they can interact does not lead me to argue the carbon should be electron deficient. The electron withdrawing property of the oxygen does. The actual acidity appears to be a combination of effects. The dimedone is lower than acetylacetone, so a ring probably increases the acidity. The OH at “A” may also increase the acidity slightly.
What is probably more interesting is the second pKa. Why should the pKa of “A” be so low?
Presumably, all of ascorbic acid becomes an enolate as the pH increases.
The enolate places a negative charge alpha to the OH as well. Presumably, our resonance isomers do not reveal the true electron withdrawing character of the vinylogous enolate to accept another negative charge, because 11 is surprisingly acidic for this dianion.
We are not using resonance and inductive in the same manner.
I am trying to model the physics of interactions. There are four forces of nature, the strong, weak, gravity, and electromagnetic. It is only electromagnetic that applies to organic chemistry. Chemists argue energy.
“Why does an energy difference exist?”
“What is the force responsible for the energy difference?”
If you have a car on a hill and one in the valley, the car on the hill has more (potential) energy due to gravity. I see electron withdrawing effects to be responsive to nuclear charge and inversely to the square of distance. That is the easy one.
If conjugation or resonance results in a lower energy state, then conjugation reflects an attractive force between electron pairs, but I didn’t just say that. What force is acting to reduce the energy state of conjugated dienes compared to non-conjugated ones?
My “complaint” was a simple one. I do not agree that a proton is acidic because you can draw a resonance structure of its conjugate base.
＊ There are four hydroxyl groups on this molecule – which one is the most acidic? If we consider all four possible conjugate bases, we find that there is only one for which we can delocalized the negative charge over two oxygen atoms.
Posted 16 hours ago, by Emily Thomas businessnewsline.com
一部のアルツハイマー病患者は1985年まで使用されてきた異常プリオンを含む成長ホルモン剤の投与によって感染していた可能性があることが9日、 University College LondonのJohn Collingeを中心とした研究チームが雑誌「Nature」を通じて発表した論文により明らかとなった。
Drinking coffee before bed may delay the human circadian rhythm by up to 40 minutes — making it more difficult to go to sleep at night, according to research published today in Science Translational Medicine.
It's the first research to show caffeine to have a direct effect on a person's internal timekeeping system. And coffee can even throw off your sleep cycle on evenings following a late-night caffeine boost, the study suggests.
It’s estimated that more than half of American adults over the age of 18 drink coffee every single day. And these coffee drinkers are consuming an average of three cups daily. Numerous studies have examined the effects of coffee’s impacts on the body, due to its high concentration of caffeine.
"Caffeine is one of the most widely consumed drugs that’s legal, but is also has these psychoactive impacts,"
says study author Dr. Tina Burke, a neuroscientist at the University of Colorado at Boulder.
However, its effect on our biological clock and internal rhythm hasn’t been well understood.
The circadian clock is a biological system that sends cues to your body telling you when you should be awake and when you should be asleep. It's controlled by a region of the brain that regulates hormonal and neural activities that trigger certain bodily functions — like sleepiness and alertness — over a 24-hour period. The circadian clock takes cues from a person's environment — that’s why, for instance, your jet lag isn’t permanent. Several things affect these rhythms but
"the biggest training cue is light; it's the primary synchronizer for the day,"
says Burke.
The clock isn't the only thing that makes you sleepy, though. There's also the homeostatic sleep-wake system, which causes the buildup of a chemical called adenosine. Adenosine inhibits processes that make you feel awake. Caffeine blocks the chemical, making you feel more alert.
But Burke and her team wanted to see if caffeine also affects the body's circadian clock, too. So Burke set up two different experiments. The first involved analyzing a group of five volunteers over a 49-day period.
The participants took a caffeine pill — equal to the amount of caffeine found in two shots of espresso — every night three hours before bed. This group was compared to people who were exposed to light before bed; it’s well known that too much light can delay a person’s sleep cycle at night. Overall, the caffeine group had their internal rhythms thrown off by 40 minutes — about half the time delay experienced by those who were exposed to light at night.
Then, Burke turned to human cell cultures. The researchers exposed cells associated with the circadian clock to high levels of caffeine in the lab. The caffeine prevented the circadian cells from signaling that it was time for sleep.
The research implies that coffee is doing more than just keeping you alert at night. It could be putting your entire rhythm out of sync. That means drinking coffee one night might have effects on your sleep cycle for many nights to come.
"You find it difficult to go to sleep at your standard desired time,"
said Dr. Timothy Roehrs, a researcher of sleep medicine at Henry Ford Hospital in Detroit, who was not involved in the study. Roehrs said this would cause people to be phase delayed, meaning it's difficult to go to sleep during your standard desired time.
"If you’re usually going to bed at 11 o’clock, it’s now midnight."
It's also possible that late-night coffee drinking is contributing to sleep issues, such as circadian sleep-wake disorders — where people can't sleep and wake up during the times the want. Because of this, Burke says people need to be much more considerate of the times they drink caffeine.
Though the study links caffeine to changes in the circadian clock, Roehrs said the cellular effects in the lab may not explain the sleep delays seen in the human subjects.
"It would be very difficult to figure out,"
he said. However, he said it makes sense that the drug is directly altering the biological clock.
"Here they are showing the inherent characteristics of the cells are being changed,"
Roehrs said.
"It’s a more direct demonstration than what has been seen before."
New pictures of Pluto released by Nasa show incredible images of rugged icy mountains and flat frozen plants as the New Horizons spacecraft looked back towards the dwarf planet at twilight.
The huge panorama, which is 780 miles wide, was captured just minutes after the Sun set over Pluto casting the final rays of light over the 11,000 feet Norgay Mountains.
The picture was taken 11,000 miles from the surface as New Horizons sailed past the icy body on July 14, the day of closest approach.
The spacecraft has collected so much data it will take 16 months to send it all back to Earth.
The mountains captured in the new images are roughly the height of The Pyrenees, but smaller ranges have been spotted on bright, heart-shaped region named Tombaugh Region.
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Nasa said the new pictures reveal a bewildering variety of surface features that have scientists reeling because of their range and complexity.
“Pluto is showing us a diversity of landforms and complexity of processes that rival anything we’ve seen in the solar system,”
said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI), Boulder, Colorado.
“If an artist had painted this Pluto before our flyby, I probably would have called it over the top — but that’s what is actually there.”
New features revealed this week include possible dunes, nitrogen ice flows that apparently oozed out of mountainous regions onto plains, and even networks of valleys that may have been carved by material flowing over Pluto’s surface.
They also show large regions that display chaotically jumbled mountains reminiscent of disrupted terrains on Jupiter’s icy moon Europa.
“The surface of Pluto is every bit as complex as that of Mars,”
said Jeff Moore, leader of the New Horizons Geology, Geophysics and Imaging (GGI) team at NASA’s Ames Research Center in Moffett Field, California.
“The randomly jumbled mountains might be huge blocks of hard water ice floating within a vast, denser, softer deposit of frozen nitrogen within the region informally named Sputnik Planum.”
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New images also show the most heavily cratered, and thus oldest, terrain yet seen by New Horizons on Pluto next to the youngest, most crater-free icy plains. There might even be a field of dark wind-blown dunes, among other possibilities.
“Seeing dunes on Pluto -- if that is what they are -- would be completely wild, because Pluto’s atmosphere today is so thin,”
said William McKinnon, a GGI deputy lead from Washington University, St. Louis.
“Either Pluto had a thicker atmosphere in the past, or some process we haven’t figured out is at work. It’s a head-scratcher.”
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Pluto is the first Kuiper Belt object visited by a mission from Earth. New Horizons will continue on its adventure deeper into the Kuiper Belt, where thousands of objects hold frozen clues as to how the solar system formed
“This bonus twilight view is a wonderful gift that Pluto has handed to us,”
said John Spencer, of the Southwest Research Institute
“Now we can study geology in terrain that we never expected to see.”
Circadian rhythms, biological processes which develop in humans by age three, span approximately 24 hours and are driven by a circadian clock (depicted below). Without environmental cues, the human circadian cycle is actually 24.2 hours.
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The retinas house photosensitive cells containing melanopsin.
These cells signal to the circadian (or biological) clock, located in suprachiasmatic nucleus in the hypothalamus, via the reticulohypothalamic tract.
These signals provide information to the brain about the length of night and day, passing it on to the pineal gland, where melatonin is then secreted.
This secretion, which is highest at night and decreases during the day, regulates the sleep-wake cycle, decreasing core body temperature and promoting sleep.
Melatonin regulates the rhythmicity of the circadian patterns of the body via yet-to-be-understood mechanisms.
The sleep cycle
In the sleep cycle, Stages 1 and 2 range between wakefulness and sleep.
Stages 3 and 4 include delta sleep, during which metabolic activity and brain waves slow, eye movements are absent, and muscle tone is atonic.
Stage 5 is characterized by bursts of rapid eye movement and dreaming, increased cerebral blood flow, and generalized muscle atonia.
