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Cis–trans isomerism

Cis–trans isomerism known as geometric isomerism or configurational isomerism, is a term used in organic chemistry. The prefixes "cis" and "trans" are from Latin: "this side of" and "the other side of", respectively. In the context of chemistry, cis indicates that the functional groups are on the same side of the carbon chain while trans conveys that functional groups are on opposing sides of the carbon chain. Cis-trans isomers are stereoisomers, that is, pairs of molecules which have the same formula but whose functional groups are rotated into a different orientation in three-dimensional space, it is not to be confused with E–Z isomerism, an absolute stereochemical description. In general, stereoisomers contain double bonds that do not rotate, or they may contain ring structures, where the rotation of bonds is restricted or prevented. Cis and trans isomers occur both in inorganic coordination complexes. Cis and trans descriptors are not used for cases of conformational isomerism where the two geometric forms interconvert, such as most open-chain single-bonded structures.

The term "geometric isomerism" is considered by IUPAC to be an obsolete synonym of "cis–trans isomerism". When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, when the substituents are oriented in opposing directions, the diastereomer is referred to as trans. An example of a small hydrocarbon displaying cis–trans isomerism is but-2-ene. Alicyclic compounds can display cis–trans isomerism; as an example of a geometric isomer due to a ring structure, consider 1,2-dichlorocyclohexane: Cis and trans isomers have different physical properties. Differences between isomers, in general, arise from the differences in the shape of the molecule or the overall dipole moment; these differences can be small, as in the case of the boiling point of straight-chain alkenes, such as pent-2-ene, 37 °C in the cis isomer and 36 °C in the trans isomer. The differences between cis and trans isomers can be larger if polar bonds are present, as in the 1,2-dichloroethenes.

The cis isomer in this case has a boiling point of 60.3 °C, while the trans isomer has a boiling point of 47.5 °C. In the cis isomer the two polar C-Cl bond dipole moments combine to give an overall molecular dipole, so that there are intermolecular dipole–dipole forces, which add to the London dispersion forces and raise the boiling point. In the trans isomer on the other hand, this does not occur because the two C−Cl bond moments cancel and the molecule has a net zero dipole; the two isomers of butenedioic acid have such large differences in properties and reactivities that they were given different names. The cis isomer is called the trans isomer fumaric acid. Polarity is key in determining relative boiling point as it causes increased intermolecular forces, thereby raising the boiling point. In the same manner, symmetry is key in determining relative melting point as it allows for better packing in the solid state if it does not alter the polarity of the molecule. One example of this is the relationship between elaidic acid.

Thus, trans alkenes, which are less polar and more symmetrical, have lower boiling points and higher melting points, cis alkenes, which are more polar and less symmetrical, have higher boiling points and lower melting points. In the case of geometric isomers that are a consequence of double bonds, and, in particular, when both substituents are the same, some general trends hold; these trends can be attributed to the fact that the dipoles of the substituents in a cis isomer will add up to give an overall molecular dipole. In a trans isomer, the dipoles of the substituents will cancel out due to being on opposite sides of the molecule. Trans isomers tend to have lower densities than their cis counterparts; as a general trend, trans alkenes tend to have higher melting points and lower solubility in inert solvents, as trans alkenes, in general, are more symmetrical than cis alkenes. Vicinal coupling constants, measured by NMR spectroscopy, are larger for trans than for cis isomers. For acyclic systems trans isomers are more stable than cis isomers.

This is due to the increased unfavorable steric interaction of the substituents in the cis isomer. Therefore, trans isomers have a less-exothermic heat of combustion, indicating higher thermochemical stability. In the Benson heat of formation group additivity dataset, cis isomers suffer a 1.10 kcal/mol stability penalty. Exceptions to this rule exist, such as 1,2-difluoroethylene, 1,2-difluorodiazene, several other halogen- and oxygen-substituted ethylenes. In these cases, the cis isomer is more stable than the trans isomer; this phenomenon is called the cis effect. The cis–trans system for naming alkene isomers should only be used when there are only two different substituents on the double bond, so there is no confusion about which substituents are being described relative to each other. For more complex cases, the cis/trans designation is based on the longest carbon chain as reflected in the root name of the molecule; the IUPAC standard designations E–Z are unambiguous in all cases, therefore are us

Uster–Oetwil tramway

The Uster–Oetwil tramway was a metre gauge rural electric tramway in the Swiss canton of Zürich. It linked the town of Uster with Oetwil in the Zürcher Oberland; the UOeB had an interchange with the main line at Uster station, on the Wallisellen to Rapperswil line. It had track connections with two other metre gauge rural lines, the Wetzikon-Meilen-Bahn, at Langholz, the Forchbahn, at Esslingen. Through the FB, the WMB had an indirect metre gauge connection to the Zürich city tram network; the line was electrified at 800 V DC. It had a length of 10.5 kilometres, with 18 stops, a maximum gradient of 7% and a minimum radius of 30 metres. Of the lines total length, all but 100 metres ran in the street; the line opened on 28 May 1909. It survived until 10 January 1949, when it was replaced by a bus service operated by the Verkehrsbetriebe Zürichsee und Oberland; the line's headquarters and workshops were located with an additional depot at Langholz. Both buildings still exists, in other uses, together with a goods shed at Mönchaltorf.

Media related to Uster–Oetwil tramway at Wikimedia Commons

2016–17 South Korean protests

2016–17 South Korean protests known as Candlelight Struggle or Candlelight Revolution, were a series of protests against President Park Geun-hye that occurred throughout South Korea from November 2016 to March 2017. After the initial demonstrations on October 26, 2016, hundreds of thousands of South Korean protesters denounced the Park administration's political scandal and called for the resignation of Park Geun-hye. Meanwhile, a series of protests led by the supporters of President Park occurred around the country as well. After the impeachment of Park Geun-hye on corruption charges in December, the pro-Park rallies mobilized thousands of protesters for counter protests. In February 2017, the Liberty Korea Party, at the time the ruling party of South Korea, claimed that the size of pro-Park rallies have begun to overwhelm the size of anti-Park rallies. In October 2016, a political scandal erupted over President Park Geun-hye's undisclosed links to Choi Soon-sil. Choi Soon-sil, a woman with no security clearance and no official position, found to have been giving secret counsel to the president.

Choi Soon-sil had known President Park since the 1970s when her father, Choi Tae-min, was former president Park Chung-hee's mentor, while the family was still grieving from the assassination of the first-lady Yuk Young-soo. Choi at that time claimed. Both have remained friends since after Park Geun-hye became president. Park's behaviour during her tenure has raised suspicions, due to her lack of communication with many parts of the government and the press. Choi, who had no official government position, was revealed to have access to confidential documents and information from the president, acted as a close confidante for the president. Choi and President Park's senior staff used their influence to extort ₩77.4 billion from Korean chaebols – family-owned large business conglomerates – setting up two media and sports-related foundations, the Mir and K-sports foundations. Choi embezzled money during the process, it is reported that some of them were used to support her daughter Chung Yoo-ra's dressage activities in Germany.

She is accused of rigging the admissions process at Ewha Womans University to help her daughter get accepted at the university. Ahn Jong-bum, a top presidential aide, was arrested for helping Choi. On October 25, 2016, Park Geun-hye publicly acknowledged her close ties with Choi. On October 28, Park dismissed key members of her top office staff and Park's opinion rating dropped to 5%, the lowest for a sitting South Korean president, her approval rating ranged from 1 to 3% for Korean citizens under 60 years of age, while it remained higher at 13% for over 60 years age group. This prompted President Park to fire members of her cabinet and the prime minister of South Korea in order to redirect the public's criticism. In particular, the sacking of the prime minister Hwang Kyo-ahn resulted in a controversy, due to the claim that his firing had been done via text message; the revelations about the relationship of Park Geun-hye and Choi Soon-sil have been resulting in mass demonstrations in Seoul known as the Park Geun-hye Resignment Pan-national Movement or Candlelight Revolution.

Protesters called for the resignation of Park Geun-hye. On October 29th, the first candlelight protest was gathered in a small size, with only 20,000 participants, but the numbers grew from the following week. On 1 November, Reuters reported a man used an excavator to crash into the front entrance of the Supreme Prosecutors' Office building during a protest in Seoul. On 5 November, people attended rally early on Saturday evening petition for Park's resignation; the police estimated 43,000, but organisers claimed more than 100,000. On 12 November, four officers were injured during the demonstrations, according to South Korea's Yonhap News Agency, which cited police. Twenty-six protesters were taken to hospital with injuries and a further 29 were treated at the scene of the protests, Yonhap quoted the Fire Department as saying. On 19 November, a large number of South Korean high school students joined the crowds after taking the college entrance test. Not all Koreans were calling for the president to resign, however.

A short drive away from the main protest, a group of conservative protesters gathered outside Seoul station in defence of the president until 17 December. On 28 November, 1.9 million people hit the streets in a nationwide anti-president rally On 3 December 2.3 million people hit the streets in a nationwide anti-president rally, the largest in the country's history. An estimated 1.6 million people gathered around the main boulevards from the City Hall to Gwanghwamun Square and Gyeongbok Palace. Another estimated 200,000 people gathered around the city of 100,000 in Gwangju. On 10 December, hundreds of thousands gathered for weekly protests cheering for the impeachment of Park Geun-hye. But, on 17 December, pro-Park supporters held their first major demonstrations in Seoul, claiming about 1 million according to the organisers, they called for the reinstatement of the impeached president. On 24 December, 550,000 people held the Christmas Santa Rally, calling for the immediate removal of their president.

On 31 December, South Koreans celebrate New Year's Eve with mass protest. Over 1 million people take to the street according to Organizer, brought the cumulative number of people who have attended the protests since October to 10 millions, the largest weekly protest in South Korean history. On the first Saturday in 2017, Hundreds of thousands of protestors ret